MACHINE   SHOP   DRAWINGS 


PUBLISHERS     OF     BOOKS      FOR./ 

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Engineering 8 Mining  Journal  v  Power 
Metallurgical  6  Chemical  Engineering 


Machine    Shop    Drawings 


READING   DRAWINGS,  MAKING   SHOP 
SKETCHES,    LAYING    OUT   WORK 


BY 

FRED  H.  COLVIN,  A.S.M.E.,  F.I. 

ASSOCIATE  EDITOR  OF  THE  AMERICAN  MACHINIST,  AUTHOR  OF  "  MACHINE  SHOP 

CALCULATIONS,"  "AMERICAN  MACHINISTS'  HANDBOOK,"  "HILL 

KINK  BOOKS,"  "RAILROAD  POCKETBOOK," 

ETC.,  ETC. 


FIRST  EDITION 
SECOND  IMPRESSION 


McGRAW-HILL  BOOK  COMPANY,  INC. 

239  WEST  39TH  STREET,  NEW  YORK 


LONDON:  HILL  PUBLISHING  CO.,  LTD. 

6  &  8-BOUVERIE  ST.,  E.  C. 

1909 


Copyright,  1909,  BY  THE  McGRAW-HiLL  BOOK  COMPANY 


The  Plimpton  Press  Norwood  Mass. 


rr 

2.30 


L  !  B  F?  /*  ^  V 

STA  t?  M-hi'/i. 
ftL  Ah  IS    »>l>   h;.iMt   CCOHOIUfcS 
ANU  BASEARA,  CALIFORNIA 


PREFACE 

THIS  little  book  is  intended  to  be  a  help  to  those  who  do 
not  thoroughly  understand  the  reading  of  drawings  rather 
than  an  attempt  to  teach  drawing  itself.  It  shows  how 
seen  and  unseen  portions  are  represented,  the  use  of  full 
and  dotted  lines,  the  way  in  which  different  views  are  drawn 
and  how  to  study  them  all  so  as  to  secure  a  correct  idea  of 
the  shape  of  the  piece  represented.  Many  actual  examples 
are  given  from  the  drawing-room  practice  of  the  leading 
shops  in  this  country  and  the  meaning  of  each  carefully 
explained. 

A  little  attention  is  given  to  laying  out  work  such  as 
gearing  of  different  kinds,  to  laying  out  angles  without  the 
aid  of  any  but  the  crudest  instruments,  and  a  number  of 
things  which  should  be  useful  in  many  ways. 
~?        The  few   examples   and   hints   in   regard   to   sketching 
k    should  also  be  of  value,  especially  to  those  of  an  inventive 
<>  turn  of  mind  or  those  who  must  convey  ideas  to  others  for 
J3  any  purpose.     In  short  it  aims  to  be  of  service  in  enabling 
^^any  one  mechanically  inclined  to  have  a  better  grasp  of  the 
^  meaning  of  working  drawings  so  that  he  can  read  them  as 
CT)  he  would  an  open  book, 
cn  THE  AUTHOR. 


Q- 

UJ 

CO 


CONTENTS 

CHAPTER  PAGE 

I    READING  DRAWINGS i 

II    DRAWINGS  OF  A  MONKEY-WRENCH 17 

III  SOME  EXAMPLES  OF  DRAWINGS .  25 

IV  HINTS  ON  LAYING  OUT 50 

V    LAYING  OUT  SPUR  GEARS 84 

VI    LAYING  Our  BEVEL  GEARS 107 

VII    THE  WORM  AND  WORM, WHEEL 113 

VIII    SKETCHES  —  ROUGH  AND  OTHERWISE 124 


vii 


MACHINE   SHOP   DRAWINGS 
CHAPTER  I 

READING   DRAWINGS 

IN  spite  of  the  fact  that  the  drawing  is  the  universal 
language  of  the  mechanic,  there  are  sometimes  differences 
of  opinions  about  the  translation  and  so  we  all  have  to 
learn  how  to  read  drawings  and  to  know  what  they  mean. 

We  are  so  accustomed  to  seeing  a  piece  of  machinery  as 
a  whole  that  it  is  not  easy  to  look  at  just  one  end  or  place 
without  regard  to  the  rest.  This  is  why  drawings  in  per- 
spective are  so  much  easier  to  understand,  and  if  a  drawing 
of  this  kind,  as  Fig.  i,  was  always  used  it  would  be  perfectly 
clear  that  a  round  bar  of  the  dimensions  given,  was  wanted. 

But  the  regular  mechanical  drawing  shows  each  side 
or  view  separately  and  this  is  why  they  are  not  as  clear  as 
the  sketch  in  perspective. 

Even  if  we  try  to  look  only  at  the  end  of  a  bar  we  are  very 
apt  to  get  the  idea  of  length  as  well  as  diameter,  when  we 
should  only  see  that  it  was  something  round  2  inches  in 
diameter,  as  at  A,  Fig.  2.  It  might  be  either  a  thin  disk 
or  a  bar  a  mile  long  as  far  as  we  know  from  this  view,  and 
it  is  necessary  to  look  at  the  side  view  B,  to  find  that  it  is 
6^  inches  long. 

Pieces  of  Uniform  Shape 

When  a  solid  piece  is  uniform  iri  one  direction,  as  round, 
square,  or  other  shaped  bar,  two  views  will  show  all  that 

i 


2  MACHINE    SHOP    DRAWINGS 

is  required,  but  these  two  are  absolutely  necessary  unless 
we  make  a  note  on  the  sketch  telling  its  other  dimension. 

If  we  look  at  B,  Fig.  3,  there  is  no  hint  as  to  whether  this 
is  a  strip  of  tin  of  this  size  or  the  end  of  a  three-foot  bar; 
but  when  we  look  at  A  we  see  that  B  is  the  side  and  A  the 


• 

-•• 

• 

-f- 

B 

FIG.  3 


Awurican  AfaeAi.uf ,  X.  K 


end  of  a  rectangular  bar  i$  inches  thick,  2$  inches  wide, 
and  5^  inches  long. 

Right  here  let  us  understand  that  on  drawings  we  rely 
on  the  figures  to  tell  the  story  and  pay  no  attention  to  the 
actual  size  of  the  drawing  itself.  If  the  dimensions  seem 
very  much  out  of  proportion,  and  you  have  your  doubts 
about  their  accuracy,  ask  the  foreman,  but  don't  attempt 


READING    DRAWINGS  3 

measuring  the   drawing;   depend  on  the  dimensions.     If 
they  are  wrong  the  fault  is  in  the  drawing  room. 

When  Three  Views  are  Needed 

So  far  we  have  dealt  with  pieces  of  uniform  shape  and  all 
has  been  plain  sailing  for  it  has  not  mattered  which  end  we 
looked  at,  tmt  with  odd  shapes  we  must  know  which  end 
is  which. 

In  this  country  we  use  what  is  called  third-angle  projec- 
tion, but  it  is  harmless  in  spite  of  its  name  and  is  easily 
explained  by  Fig.  4. 

The  upper  sketch  shows  two  views  of  the  same  piece  in 
perspective.  If  your  eye  was  at  A,  looking  at  the  end  B, 
and  you  swung  the  end  to  the  right,  it  would  appear  as  at  C. 
The  view  in  the  direction  of  the  arrow  D  would  be  the  front 
view  as  seen  at  D'  in  the  center  of  the  lower  views. 

Swinging  the  end  B'  around  to  the  right  shows  it  like  C', 
and  swinging  E  to  the  left  gives  Ef.  The  line  ab  shows 
that  there  is  a  change  in  surface  at  this  point,  but  without 
the  end  views  we  would  not  know  that  it  was  a  large  flat 
surface  running  back  to  the  raised  edge  or  lip  F.  In  a 
similar  way  the  dotted  lines  cd  and  ef  show  a  change  back 
of  the  front  surface  .and  not  visible  from  it.  The  end 
views  show  this  to  be  a  hole  through  the  piece  of  the  shape 
indicated  by  GG.  These  will  be  taken  up  a  little  later. 

For  the  present,  just  fix  in  your  mind  that  the  view  given 
at  the  right  of  the  front  or  side  of  a  piece  is  just  what  you 
would  see  if  you  looked  squarely  at  that  end.  The  same  is 
true  of  the  other  end,  and  of  the  top  and  bottom  views 
when  they  are  necessary.  The  top  view  shows  just  what 
you  would  see  if  you  looked  down  on  it,  and  the  bottom 


MACHINE   SHOP    DRAWINGS 


li. 

0, 

J 

»       -o     ^.  "on 

b 

^ 

0- 

FIG.  4.  —  The  Way  Views  are  Placed. 


READING    DRAWINGS  5 

view  just  as  it  would  appear  from  underneath.  The  top 
view  is  usually  called  the  "plan"  view  because  in  most 
cases  it  gives  the  general  plan  or  idea  of  a  machine  or  a 
building. 

Points  to  Remember 

There  are  two  or  three  points  to  fix  in  your  mind  that 
will  help  in  reading  any  drawing. 

Even'  solid  line  shows  a  change  in  the  surface  you  see 
of  the  object  drawn,  and  the  other  views  should  show  what 
this  change  is. 

Every  dotted  line  indicates  a  change  in  some  surface  that 
cannot  be  seen,  and  dotted  lines  are  used  to  show  that 
openings  occur  beyond  the  surface  seen,  or  the  shape  of 
the  back  or  under  side  of  the  piece.  The  only  exception 
to  this  is  the  center  line,  which  is  sometimes  drawn.  This 
should  always  be  drawn  with  a  long  dash  and  a  dot,  while 
the  regular  dotted  line  is  a  broken  line  with  dashes  of  even 
lengths.  The  center  line  does  not  indicate  a  change  of 
shape,  but  is  generally  used  to  measure  from  or  to  locate 
points. 

Shade  Lines 

Shade  lines,  that  is,  lines  made  heavier  than  the  rest  of 
the  drawing,  are  used  to  show  at  a  glance  which  is  the  top 
or  bottom  of  the  drawing.  The  light  is  always  supposed 
to  come  down  from  the  upper  left-hand  corner  of  the  paper. 
This  would  throw  the  bottom  and  right-hand  end  in  a 
shadow  and  these  lines  are  made  heavier  to  show  that  this 
is  the  case.  This  is  not  always  done,  however,  and  is  not 
really  necessary,  as  there  is  almost  always  a  title,  or  letters 


6  MACHINE    SHOP    DRAWINGS 

or  figures  which  show  the  top  and  bottom.  But  if  the 
drawing  has  heavy  shade  lines,  you  can  tell  at  once  which  is 
the  bottom  and  which  the  top. 

Figs.  5  and  6  show  this.  If  either  of  them  were  handed 
you,  bottom  side  up  and  without  any  lettering,  you  would 
know  which  way  they  belonged  by  these  heavy  lines. 

The  front  view  of  Fig.  5  shows  three  lines,  A,  B  and  C, 
each  indicating  some  change  in  the  surface  at  these  points. 
What  these  changes  are  must  be  told  by  the  end  views.  It 
may  be  like  D,  with  even  steps  cut  in  the  side;  or  like  E, 
with  smaller  steps;  or  even  like  F,  shown  at  the  other  end 
where  there  are  no  steps,  but  inclined  surfaces  between 
the  top  and  A,  and  between  B  and  C,  while  between  A  and 
B  there  is  a  groove,  as  shown,  and  with  different  angles. 

The  front  view  of  Fig.  6  shows  a  rectangle  with  a  line 
across  the  face  at  A  B.  This  might  mean  any  one  of  a  dozen 
shapes,  but  referring  to  E  shows  us  that  the  end  C,  up  to 
the  line  AB,  is  cut  away  at  an  angle  of  45  degrees,  as  shown. 
The  view  F  at  the  other  end  shows  D  to  be  square  and  the 
dotted  line  in  F  indicates  the  cutting  away  at  the  other  end. 

The  line  A  B  across  the  front  shows  it  to  be  a  square  cut, 
while  if  it  had  been  rounded  out  as  with  a  milling  cutter 
there  would  be  no  straight  line  AB,  but  a  solid  curved  line, 
as  shown  dotted  on  D,  and  as  shown,  also  dotted,  on  the 
small  sketch  at  the  right  which  gives  a  view  of  the  piece  in 
perspective. 

Where  Five  Views  are  Needed 

The  next  example,  Fig.  7,  requires  five  views  to  show  the 
piece.  The  central  view  A  is  the  "  plan,"  or  view  looking  at 
the  top  of  the  piece,  and  gives  very  little  idea  of  it,  except  that 


READING    DRAWINGS 


8  MACHINE    SHOP    DRAWINGS 

the  total  length  is  3!  inches,  the  width  is  i  inch,  that  there  is 
some  sort  of  a  rib  or  perhaps  a  groove,  £  inch  wide  and  f  inch 
from  one  edge,  while  lines  ab  and  cd  show  a  change  of  shape 
of  this  rib  or  groove,  whichever  it  proves  to  be,  but  gives 
no  information  about  it.  The  dotted  lines  indicate  a  de- 
pression of  some  kind  in  the  upper  side  and  the  dot-and- 
dash  line  shows  the  center  line  of  the  piece,  showing  that  the 
widest  part  is  considered  as  the  main  part  of  the  piece. 

Going  to  the  right-hand  view  B,  we  find  that  the  base  is 
a  flange  §  inch  thick,  and  we  know  from  the  first  view 
that  the  width  is  i  inch.  This  shows  that  the  two  parallel 
lines  indicated  a  rib  £  inch  thick,  that  the  upper  side  of 
this  is  fy  inch  from  upper  edge  of  flange,  that  the  rib  pro- 
jects if  inches  above  the  flange  at  this  end,  that  the  total 
hight  is  1 1  inches,  and  that  the  depression  indicated  by 
dotted  lines  is  W  mc^  deep. 

The  other  end  C  is  similar  except  that  the  total  hight  is 
i$  inches,  the  rest  of  the  dimensions  being  the  same.  There 
is  no  need  of  repeating  similar  dimensions  as  they  are  always 
the  same  in  all  views. 

The  upper  view  D  means  simply  that  the  back  edge  of 
the  piece,  as  seen  in  the  plan  view  A,  is  raised  until  it  is 
vertical,  and  it  will  then  show  as  in  D,  with  the  flange  on 
top.  This  shows  that  the  top  of  rib  is  a  plain  taper  from 
a  hight  of  1 1  inches  to  ij  inches  above  the  flange  (these 
dimensions  being  shown  in  views  B  and  C),  that  the  left- 
hand  upper  edge  is  VV  mcn  from  this  end  of  the  base  flange, 
and  the  right  -ft-  inch  from  the  other  end,  with  the  top  of 
the  rib  3^  inches  long  measured  parallel  with  the  bottom 
flange  (or  top  in  this  view). 

This  view  shows  that  the  depression  is  in  the  top  of  the 


READING    DRAWINGS  9 

rib,  as  shown  in  the  plan  view  A,  the  full  lines  showing  it 
to  be  on  this  side.  The  long  side  of  this  depression  is 
shown  parallel  with  the  flange  of  the  base  and  ft  inch  from 
it.  The  right-hand  end  is  i  inch  from  the  end  of  the  flange, 


/, 

/     \  " 

1 

1 

1 

H                                    J 

FIG.  7.  —  A  Piece  where  Five  Views  are  Needed. 

the  greatest  hight  or  width  being  |£  inch,  the  other  point 
i  inch  and  the  length  of  the  various  parts  f  inch,  i  inch  and 
£  inch,  as  shown. 

The  view  from  the  wide  side  is  shown  at  E,  where  the 
back  edge  is  pulled  down  instead  of  up.     The  dotted  lines 


I0  MACHINE    SHOP    DRAWINGS 

show  that  some  change  takes  place  in  the  piece  beyond 
the  surface  that  can  be  seen,  but  does  not  tell  whether  it 
is  a  depression  or  a  projection  of  this  shape.  We  must 
depend  on  the  other  yiews  for  this  part  of  the  story. 


,y.r. 

'  FIG.  8.  —  How  Pieces  Appear  in  Different  Positions. 

The  way  in  which  these  views  are  drawn  out  can  perhaps 
be  seen  to  better  advantage  in  Fig.  8.  This  shows  just  why 
the  top  view  seems  to  be  upside  down  and  why  the  end 
views  seem  to  be  lying  on  their  sides. 


READING    DRAWINGS  H 

Going  back  to  Fig.  7,  and  calling  E  the  plan  view,  the 
end  views  would  then  be  as  shown  at  F  and  G,  and  the 
bottom  views  as  at  H.  But  neither  A,  E,  F,  G  nor  H 
show  the  depression  in  solid  lines,  so  that  D  would  be  neces- 
sary in  any  case.  But  we  would  then  draw  it  below  H, 
in  just  the  same  way  as  E  is  placed  below  A  when  that  was 
drawn  as  the  plan  or  top  view. 

Other  Examples 

In  Figs.  9,  10  and  n  we  have  other  Wamples  which  will 
serve  to  show  a  little  more  what  we  find  in  the  shop,  the 
first  being  a  common  lathe  center.  The  taper  is  4  inches 
long,  |  inch  at  the  small  end  and  i  inch  at  the  large  end. 
Looking  at  the  end  view  we  find  that  the  part  marked  if 
inches  is  square  and  £  inch  thick.  The  end  view  shows 
the  front  end  to  be  round  and  the  side  view  indicates  a 
6o-degree  cone,  while  the  dotted  circle  shows  simply  the 
small  end  of  the  long  taper. 

If  it  were  not  for  the  end  view  there  would  be  nothing 
to  show  what  shape  the  piece  was  round  and  it  might  easily 
be  such  a  shape  as  shown  at  the  extreme  right. 

Fig.  10  shows  a  socket  or  holder  for  a  turret  lathe  or 
similar  purpose.  The  side  view  shows  a  piece  6  inches 
long  by  1 1  inches  diameter.  The  dotted  lines  at  the  left 
indicate  some  kind  of  an  opening  and  the  dotted  circle 
in  the  end  view  shows  this  to  be  a  round  hole.  This  has  a 
round  hole  at  right  angles  with  a  larger  hole  on  one  side 
than  the  other,  the  large  hole  being  next  the  observer  so 
the  small  hole  shows  straight  through  the  large  one. 

The  other  end  is  broken  away,  showing  the  hole  in  solid 
lines  and  the  metal  around  it  in  section  lining.  In  some 


MACHINE    SHOP    DRAWINGS 


A   Few  Common  Examples  from  the  Shop. 


READING    DRAWINGS  13 

drawings  the  kind  of  lines  indicate  the  metal  to  be  used, 
while  in  some  cases,  as  the  one  shown,  the  material  is 
shown  by  its  name  or  by  letters,  as  M.S.  for  machinery 
steel.  The  broken  section  shows  the  hole  to  be  if  inches 
in  diameter  and  that  both  holes  are  ij  inches  deep. 

It  will  be  noted  that  the  upper  wall  is  not  as  thick  as 
the  lower  one,  and  while  this  might  mean  that  the  hole 
was  eccentric  in  the  bar,  as  shown  at  the  extreme  right, 
the  end  view  shows  the  hole  to  be  central,  but  that  the  top 
of  the  bar  is  flattened  to  allow  it  to  be  held  by  a  key. 

Fig.  ii  takes  three  views  to  show,  and  from  the  left  and 
center  views  we  find  that  there  is  a  round  shank  i£  inches 
in  diameter  and  2\  inches,  long.  The  two  end  views  show 
the  shape  of  the  head  and  give  dimensions  of  the  slope, 
the  lip  and  the  other  parts.  The  center  of  the  shank  is 
|  inch  from  one  edge  and  i|  inches  from  the  other  edge, 
although  the  latter  dimension  is  hardly  necessary,  as  by 
taking  J  inch  from  the  total,  2\  inches,  we  have  i£  inches. 

So  far  we  have  not  touched  on  threads  or  gears,  assembly, 
or  real  working  drawings,  but  these  will  come  at  another 
time. 

The  Nut  and  Bolt 

One  of  the  most  common  things  in  the  shop  is  the  nut, 
either  square  or  hexagon,  and  it  makes  a  good  example  of 
how  things  are  drawn  out  on  paper.  We  must  remember 
that  we  look  only  from  one  side  at  a  time  and  must  see 
nothing  else,  so  a  square  nut  will  show  either  one  flat  side, 
if  we  look  at  it  squarely,  or  parts  of  two  sides  if  we  look 
toward  one  corner.  This  corner  could  be  in  any  position, 
but  is  always  taken  as  being  in  the  center  as  in  B,  Fig.  i  la. 


I4  MACHINE   SHOP   DRAWINGS 

A  shows  the  flat  side  of  a  nut  without  chamfer  or  bevel, 
while  in  B  we  see  the  corner  in  the  center  and  the  top  views 
show  the  position  of  the  nuts.  The  total  distance  across 
the  nut  in  B  is  the  long  diameter  or  diagonal  of  the  square. 


D  rrrri  rrn 


FIG.  ua.  —  Different  Views  of  Nuts. 

In  C  we  have  a  hexagon  nut  with  one  corner  toward  it  so 
that  it  looks  like  the  Square  nut  until  we  see  the  top  view. 
D  is  the  proper  way  to  show  a  hexagon  nut,  with  the  two 
corners  to  the  front.  The  extreme  width  is  always  twice 
the  length  of  one  side,  and  the  middle  flat  is  equal  to  both 
the  others  as  they  appear  in  this  view.  This  is  shown  by 


READING    DRAWINGS  15 

the  dotted  lines  coming  down  as  in  D.  In  laying  out  a 
hexagon  nut  we  divide  the  whole  thing  into  four  parts,, 
put  one  part  at  each  side  and  leave  the  two  parts  in  the 
middle. 

A  square  nut  is  always  represented  as  having  one  corner 
in  the  center,  and  in  a  hexagon  we  always  see  two  corners. 
Remembering  this  we  can  tell  without  a  top  view  whether 
a  square  or  hexagon  nut  is  wanted. 


FIG.  nb.  —  Bolts  and  Broken  Sections. 


So  far  we  have  shown  plain,  flat  nuts  with  no  bevels  or 
chamfer.  This  is  usually  drawn  as  shown  in  E  and  F. 
The  thickness  of  the  nut  is  usually  the  same  as  the  bolt 
diameter  and  it  is  customary  to  lay  out  the  curve  showing 
the  bevel  as  shown.  The  centers  for  the  curves  are  shown 
in  both  side  views.  Bolt  heads  are  drawn  in  a  similar 
way,  the  size  being  somewhat  smaller  as  can  be  seen  from 
any  bolt  table. 


X6  MACHINE   SHOP    DRAWINGS 

Broken  Sections 

When  showing  bolts  and  nuts  it  often  happens  that  we 
want  to  use  a  fairly  large  scale,  but  find  this  will  take  up 
too  much  room  if  it  is  a  long  bolt.  So  we  show  the  head 
and  nut  ends  of  the  bolt  as  large  as  we  want  to  and  cut 
the  bolt  in  two  as  in  G,  Fig.  nb.  By  giving  the  length  in 
the  dimension  line  A  the  same  drawing  might  answer  for  any 
length  bolt  of  this  size.  The  broken  ends  are  usually  shown 
in  the  style  given  in  G,  although  sometimes  a  section  of  the 
bolt  itself  is  given,  as  in  H .  This  is  also  used  where  bolts 
or  rods  of  irregular  shape  are  used  as  in  7  and  /.  The  first 
is  a  flattened  section,  while  the  other  is  sort  of  an  H-section. 
This  is  a  handy  way  in  many  cases  and  shows  the  shape 
better  than  in  almost  any  other  way.  It  also  enables  the 
dimensions  of  the  cross-section  to  be  given  if  desired,  as  is 
usually  the  case. 


CHAPTER  II 

DRAWINGS   OF   A  MONKEY-WRENCH 

EVERY  tool  or  piece  of  machinery  having  more  than  one 
piece  requires  an  assembly  and  a  detail  drawing  unless  it 
is  so  simple  as  to  be  very  clear  from  the  one  view.  But 
even  in  this  case  it  is  hard  to  put  dimensions  on  such  a 
drawing,  which  is  confusing  where  the  whole  thing  is  shown 
together. 

The  assembly  drawing  shows  the  whole  machine  put 
together  with  no  dimensions  except  at  times  the  distances 
from  one  part  to  the  other.  The  separate  parts  are  shown 
in  detail  on  detail  drawings  and  all  dimensions  given. 
Fig.  12  is  a  monkey-wrench  in  perspective  showing  all  the 
parts  in  place,  while  in  Fig.  13  all  the  parts  are  shown  in 
three  views  but  without  dimensions.  A  regular  working 
drawing  would  show  all  the  dimensions  as  we  shall  see  later. 

Beginning  with  the  main  bar  of  the  wrench  we  find  there  is 
a  side  view  as  shown  at  A ,  giving  the  shape  and  proportions 
of  the  head,  the  slide  or  rectangular  portion  as  shown  from 
B,  while  C  shows  the  end  of  the  head.  Although  there  is 
nothing  to  show  that  the  end  handle  is  round,  we  know 
it  is  from  the  round  hole  in  the  handle  M  as  shown  at  N 
and  O.  The  sliding  jaw  is  shown  at  D,  E  and  F,  and  study- 
ing all  three  we  see  that  it  has  a  rectangular  hole  through 
it  to  fit  the  bar  and  that  it  is  threaded  for  the  screw. 
17 


i8 


MACHINE    SHOP    DRAWINGS 


Although  the  side  view  shows  the  thread  in  dotted  lines, 
the  end  view  in  F  also  shows  this  by  the  two  circles,  one 
representing  the  bottom  and  the  other  the  top  of  the  threads. 

The  thrust  piece  G  shows  the  holes  in  dotted  lines,  but  H 
shows  the  recess  to  be  rectangular  to  fit  the  bar,  while  the 
other  end  of  this  hole  is  round.  The  back  end  of  the  screw 


FIG.  12.  —  A  Monkey- Wrench  in  Perspective. 

fits  into  the  small  round  recess  which  holds  it  in  place. 
The  nut  /,  which  goes  on  the  end  of  the  handle,  is  also 
shown  in  three  views,  showing  that  it  is  taper,  is  threaded, 
and  has  a  slot  across  the  end  for  a  special  screw-driver. 
The  handle  M  in  this  case  is  not  shown  exactly  round  as 
can  be  seen  from  the  end  views  N  and  O.  The  screw 
needs  no  explanation  as  the  question  of  thread  will  be 
taken  up  later. 


DRAWINGS    OF   A    MONKEY-WRENCH  19 

^ 

o 


20  MACHINE    SHOP    DRAWINGS 

The  next  illustration,  Fig.  14,  shows  a  few  details  of 
this  wrench,  such  as  you  would  get  on  a  shop  "card," 
made  from  a  blue-print  pasted  to  a  piece  of  cardboard' or 
sheet  metal  and  probably  shellacked  or  varnished  so  it  will 
not  be  soiled  and  injured.  This  is  not  taken  from  the 
drawings  of  any  wrench  maker  and  all  the  dimensions  are 
assumed  for  the  occasion,  but  they  serve  to  show  how  such 
drawings  are  made. 

This  "card"  or  drawing,  should  contain  all  the  dimen- 
sions necessary  to  go  ahead  and  make  these  parts  of  the 
wrench.  Beginning  with  the  main  jaw  or  bar,  we  find  that 
the  head  is  z\  inches  long,  i  inch  wide,  \  inch  thick  and 
that  the  point  tapers  down  to  \  inch;  beginning  i  inch  back 
from  the  point. 

The  bar  is  set  \  inch  from  the  back  of  the  head  and  set 
central  to  the  width  of  the  jaw,  leaving  \\  inches  from 
the  bar  to  the  end  of  the  jaw.  The  straight  or  rectangular 
part  of  the  jaw  is  i  X  \  inch,  as  can  be  found  from  the  side 
and  left  end  views,  and  6J  inches  long.  The  rest  is  round, 
\  inch  in  diameter  for  4  inches,  Jv  inch  on  the  end  and 
threaded  14  to  the  inch,  U.  S.  S.  thread.  This  part  is 
i  inch  long.  Adding  up  the  different  parts  we  find  the 
total  length  is  12  inches. 

Here  is  where  mistakes  are  liable  to  creep  in  and  it  is 
well  to  look  at  a  drawing  carefully  to  make  sure  the  dimen- 
sions agree.  While  it  is  true  that  any  mistake  in  the  draw- 
ing is  "on"  the  draftsman  and  is  not  your  fault,  still  it  is 
better  in  every  way  to  avoid  spoiling  work  or  getting  some 
one  else  into  trouble. 

The  recess  for  the  nurled  end  of  the  screw  is  shown  to 
be  ft  inch  long  and  -^  inch  deep.  -  This  is  for  the  nurled 


DRAWINGS    OF   A    MONKEY-WRENCH 


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22  MACHINE    SHOP    DRAWINGS 

head  to  turn  in  and  also  prevents  the  jaw  from  sliding 
along  the  bar.  It  is  to  be  cut  with  a  milling  cutter,  2  inches 
in  diameter,  which  gives  a  curve  of  i  inch  radius  as  shown 
in  the  end  view. 

Coming  to  the  sliding  jaw  we  find  dimensions  a  little 
more  .complicated.  The  total  hight  is  the  same  as  the 
length,  2\  inches.  The  jaw  is  i  inch  wide,  while  the  hole 
is  fa  by  sV  inch.  Comparing  this  with  the  bar  we  see  it 
allows  3^  inch  clearance  both  ways,  ^  inch  on  all  sides. 
The  back  end  of  the  jaw  is  \\  inches  high,  the  hole  is  2 
inches  long,  tapped  with  a  J-inch,  square  thread  tap,  6  to 
the  inch.  The  jaw  point  is  \  inch  deep,  the  distance 
across  the  center  ij  inches,  with  \  inch  cut  away  at  the 
back.  The  lower  view  shows  the  sliding  jaw  from  the 
back,  giving  the  thickness  as  \  inch  through  the  middle 
portion. 

The  lettering  in  the  corner  varies  with  the  idea  of  the 
draftsman,  the  system  of  numbering  the  drawings  or 
"cards"  being  different  in  almost  every  shop. 

Tabulated  Drawings 

Another  plan  used  in  some  shops  is  to  make  one  drawing 
answer  for  several  sizes  by  using  a  table  as  shown  in  Fig.  15 
in  connection  with  the  drawing.  All  the  dimensions  are 
lettered  and  the  size  of  each  part  given  in  the  table  under 
its  proper  letter.  Thus  M  represents  the  total  length  of 
the  bar  and  is  6,  8,  10  and  12  inches  long  according  to  the 
size.  If  you  are  working  on  a  6-inch  wrench,  all  the  dimen- 
sions are  given  in  the  upper  line,  the  loinch  wrench  sizes 
are  in  the  third  line,  and  so  on. 

While  this  saves  a  drawing  for  each  of  the  other  three 


DRAWINGS    OF   A    MONKEY-WRENCH 


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sizes,  it  is  considerable  work  making  the  table  and  to  get 
it  absolutely  correct,  and  it  is  much  harder  to  work  to  than 
the  separate  drawings  because  it  is  very  easy  to  take  a 
dimension  from  the  wrong  line  and  so  make  a  mistake. 

It  is  a  very  convenient  way  to  make  reference  drawings 
for  the  superintendent  or  chief  draftsman,  but  it  is  not  as 
easy  to  work  from  as  the  separate  working  drawing  and  is 
not  generally  used  on  this  account. 


CHAPTER  III 

SOME   EXAMPLES    OF    DRAWINGS 

As  the  best  way  to  learn  a  thing  is  by  doing  it,  so  the  best 
way  to  read  drawings  is  by  taking  some  actual  cases  and 
examine  them  in  detail  to  find  out  just  what  they  mean. 
The  examples  have  been  taken  from  a  great  variety  of 
sources  in  order  to  show  the  practice  in  different  shops 
and  also  to  give  an  idea  of  the  different  classes  of  work.  In 
this  way  many  will  find  the  kind  of  work  that  interests 
them  most  and  perhaps  understand  the  drawings  a  little 
easier  on  that  account.  These  are  taken  from  the  draw- 
ings of  some  of  the  best  firms  in  the  country  and  show  how 
ideas  are  put  on  paper  either  for  illustration  or  to  work  to. 

Details  of  a  Bench  Lathe  Head 

One  of  the  great  satisfactions  of  knowing  how  to  read 
drawings  is  the  ability  to  see  just  how  all  kinds  of  machinery 
is  constructed  without  ever  having  seen  the  machine  itself. 
Of  course  we  do  not  always  get  things  pictured  in  our 
minds  in  the  right  proportions  even  where  dimensions  are 
given,  unless  we  are  careful  to  compare  different  parts  with 
other  machines  that  we  are  familiar  with,  but  the  way  any 
machine  is  built  is  always  at  our  disposal  if  we  can  see  the 
drawings  of  it. 

Fig.  1 6  is  the  head  of  a  Cataract  bench  lathe  and  is  a 
good  example  for  study. 

25 


26 


MACHINE    SHOP    DRAWINGS 


SOME    EXAMPLES    OF    DRAWINGS 


27 


The  spring  collet  or  draw-in  chuck  is  plainly  shown  at  A 
with  its  back  end  threaded  inside  the  draw-in  tube  C 
which  has  the  handled  fastened  to  the  back  end.  Both 
collet  and  draw-in  tube  are  inside  the  lathe  spindle  B. 
The  bearings  are  not  shown  in  detail  but  are  of  the  cone 
type,  split  on  one  side  so  as  to  take  up  wear  as  they  are 
forced  into  the  taper  hole  on  the  head,  outside  the  spindle. 
The  threaded  caps  II  force  the  bearings  in  and  at  the  same 
time  act  as  dust  guards  to  keep  dirt  out  of  the  bearings. 
These  bearings  are  oiled  by  the  wicks  shown,  which  evi- 
dently lead  up  from  oil  reservoirs  to  the  bearings.  Although 
the  one  at  the  back  seems  to  touch  the  index  pin  H,  common 
sense  tells  us  this  is  not  the  case  as  the  oil  would  work  out 
around  the  pin  and  the  index  holes  do  not  need  lubricating. 
Although  it  is  not  shown,  we  can  feel  very  sure  that  the  oil 
wick  is  about  in  the  center  of  the  head  and  the  index  pin 
at  one  side,  toward  the  front  so  as  to  be  convenient  to  use. 

The  cone  E  is  fastened  to  the  hollow  spindle  by  the  two 
conical  pointed  set  screws  at  opposite  side,  and  it  would 
appear  that,  by  removing  these  set  screws  so  as  to  clear 
the  spindle  and  by  taking  out  the  draw-in  tube,  that  the 
whole  spindle  could  be  drawn  out  through  the  front  bear- 
ing. The  cone  has  two  sets  of  holes,  one  in  the  front  and 
the  other  in  the  rear  flange.  The  front  holes  are  for  lock- 
ing the  head  while  unscrewing  the  collet  or  taking  off 
chucks,  while  the  rear  set  are  kept  for  accurate  indexing 
and  not  used  for  anything  else. 

Instead  of  having  thrust  collars  on  the  spindle  as  in  most 
makes  of  larger  lathes,  the  thrust  is  taken  up  in  the  cone 
itself  by  the  ball-thrust  bearing  shown  at  G.  This  is 
adjusted  by  the  nut  F  with  the  pin  holes  for  a  wrench 


28  MACHINE    SHOP    DRAWINGS 

put  in  at  the  angle  shown.  This  allows  the  ball  races 
to  be  adjusted  so  that  there  will  be  no  shake  in  the  head, 
and  the  balls  take  all  the  thrust  of  drilling  and  boring. 

No' thread  is  seen  on  the  nose  of  the  spindle  and  the  small 
cut  at  J  shows  how  the  chucks  and  face  plates  are  held  in. 
The  nose  is  turned  to  a  taper  and  has  what  is  practically 
a  double  bayonet  joint.  This  slot  is  milled  in  from  the 
front  and  then  at  the  angle  shown  to  each  side.  The  chuck 
or  face  plate  carries  a  pin  that  slips  in  the  slot  and  is  held 
firmly  or\  the  taper  nose  by  being  drawn  in  close  contact  by 
the  incline  of  the  side  slots. 

A  Large  Lathe  Head 

A  decided  contrast  with  the  bench  lathe  is  the  large  lathe 
head  shown  in  Fig.  17  where  the  main  bearing  is  30  inches 
in  diameter  and  24  inches  long  while  the  rear  bearing  is 
1 6  inches  in  diameter  and  18  inches  long.  The  spindle  is 
hollow  and  has  an  8-inch  bar  running  through  it  which 
carries  a  boring  and  facing  head  on  the  outer  end  for  bor- 
ing the  hole  and  facing  the  hub  of  fly  wheels  while  they  are 
being  turned  on  the  large  face  plate.  This  allows  the  bor- 
ing bar  to  be  run  at  the  proper  boring  speed  independent  of 
the  slow  speed  necessary  in  facing  or  turning  the  rim. 

The  motor  drive  is  interesting,  coming  from  the  motor 
with  its  i6-tooth  pinion  and  driving  the  ii2-tooth  gear 
below  it.  This  drives  out  to  the  right  while  the  i8-tooth 
pinion  here  drives  the  io8-tooth  gear  driving  the  ao-tooth 
pinion  at  the  left.  From  here  a  shaft  (not  shown,  but 
we  know  the  face  plate  must  be  driven  somehow  and  that 
it  must  come  from  this)  runs  to  the  face  plate  at  the  right 
and  meshes  in  the  teeth  in  its  outer  edge.  The  first  driven 


SOME    EXAMPLES    OF    DRAWINGS  29 


FIG.  17.  —  Head  of  a  Large  Lathe. 


3o  MACHINE    SHOP    DRAWINGS 

shaft  runs  to  the  left  as  well  as  the  right  and  carries  a  tight 
and  loose  pulley  for  driving  the  feed  of  the  boring  and  fac- 
ing bar  inside  the  spindle.  The  first  pair  of  gears  are  next 
to  the  pulleys  on  the  upper  shaft  while  the  next  pair  are 
at  the  end  of  the  rear  bearing,  the  pinion  showing  in  full, 
but  part  of  the  gear  being  hidden  behind  the  bar.  This 
drives  the  shaft  running  to  the  left  and  its  gears  drive  the 
screw  behind  the  bar,  using  either  set  desired  and  allowing 
the  rear  set  to  be  changed  at  will  to  secure  special  feeds. 
Throwing  the  belt  on  the  loose  pulley  allows  the  feed  to  be 
operated  by  hand,  using  the  handle  at  the  extreme  left. 

This  is  not  a  regular  working  drawing  as  it  does  not  give 
all  dimensions  but  only  the  main  ones  and  the  general 
layout  scheme  for  the  head.  This  is  the  kind  of  a  drawing 
or  sketch  (for  it  would  not  be  made  as  carefully  as  is  here 
shown)  that  would  be  handed  over  to  the  draftsman  to 
have  the  details  worked  out,  the  chief  having  decided  on 
the  speeds  and  gear  ratios  of  the*  different  parts  as  well 
as  the  main  dimensions  such  as  the  swing  and  the  bearings. 

General  Locomotive  Details 

To  show  how  a  few  dimensions  give  a  good  idea  of  the 
main  points  of  a  locomotive,  we  can  refer  to  Fig.  18,  show- 
ing an  oil-burning  Vauclain  compound  as  built  by  the 
Baldwin  Locomotive  Works.  The  high-pressure  cylinder  is 
17  X  32  inches  and  the  low  28  X  32  inches.  The  center  of 
boiler  is  9  feet  2  inches  above  the  rail  and  the  boiler  6  feet 
2  inches  in  diameter.  The  pilot  is  4  feet  \  inch  long,  dis- 
tance from  pilot  to  center  of  truck  wheel  2  feet  9  inches,  and 
the  truck  wheel  is  3  feet  8  inches  in  front  of  center  of  cylin- 
der, while  the  forward  driver  is  5  feet  6  inches  behind  this. 


SOME    EXAMPLES    OF    DRAWINGS 


3  2  MACHINE    SHOP    DRAWINGS 

The  driving-wheel  centers  are  5  feet  i  and  5  feet  2  inches, 
while  from  center  of  rear  drivers  to  back  end  of  engine 
is  8  feet  5^  inches.  The  driving-wheel  base,  the  distance 
between  centers  of  rear  and  forward  drivers,  is  15  feet  4 
inches,  while  the  total  engine  wheel  base  is  24  feet  6  inches, 
and  the  total  wheel  base  for  engine  and  tender  is  54  feet 
2\  inches.  The  engine  truck  wheel  is  2  feet  6  inches, 
tender  trucks  2  feet  ioj  inches  and  the  drivers  4  feet  9 
inches.  Tender  truck  distances  are  shown  as  are  the  oil 
and  water  capacities  of  the  tender. 

A  little  familiarity  with  reading  drawings  makes  much 
information  of  this  kind  available  which  is  not  otherwise 
understandable. 


A  French  Drawing 

Just  to  show  that  drawings  are  a  universal  language,  take 
the  one  shown  in  Fig.  19  of  a  worm  shaft  fitted  with  ball 
bearings.  The  worm  is  shown  at  W,  in  the  center  of  the 
shaft.  At  each  end  are  dust  and  oil  guards  A  A,  which  fit 
into  grooves  in  the  case,  showing,  if  we  did  not  know  from 
experience  that  the  case  is  in  two  pieces  and  put  together 
in  some  way,  presumably  bolted. 

There  are  three  sets  of  ball  bearings,  BBB,  the  one  at 
the  left  being  a  thrust  bearing  with  curved  ball  races  at 
each  side  to  allow  for  any  movement  of  the  shaft  out  of 
center.  The  balls  are  held  in  place  by  the  retaining  rings 
DD  while  the  races  CC  take  all  the  end  thrust  of  the  worm 
in  either  direction.  The  other  bearings  support  the  shaft 
and  EE  are  further  oil  guards  to  keep  the  bearing  oil  in 
the  cases,  and  the  grease  or  other  lubricant,  used  for  the 


SOME    EXAMPLES    OF    DRAWINGS 


33 


34 


MACHINE    SHOP    DRAWINGS 


worm,  out  of  the  bearings.     The  bearings  are  oiled  through 
the  small  oil  cups  at  the  top. 

The  dimensions  are  in  millimeters,  which  may  be  con- 
fusing, but  there  is  no  trouble  in  knowing  just  what  is 
meant  by  the  drawings  even  if  we  do  not  understand  the 
dimensions.  Calling  a  millimeter  .039  of  an  inch,  which 
is  near  enough  for  most  cases,  all  you  have  to  do  is  to  mul- 
tiply the  figures  given  by  .039  and  you  have  the  dimensions 
in  inches. 

Grinder  Spindle  Details 

An  example  of  considerable  more  detail  in  a  small  space 
is  in  the  internal  grinding  spindles  of  the  Bath  grinder 
shown  in  Fig.  20.  The  middle  view  is  the  regular  spindle 
with  its  main  support  A  having  a  large  and  substantial 
flange  for  fastening  to  the  head  of  the  machine,  the  exten- 
sion support  B,  which  carries  the  bearings  and  steadies  the 
spindle  clear  to  the  work.  The  grinding  spindle  proper  is 
C,  having  a  tapered  end  for  holding  the  wheel  bushing  E, 
carrying  the  wheel  W  and  held  in  place  by  the  washer  F 
and  the  nut  G.  It  will  be  seen  that  the  spindle  is  not  con- 
tinuous but  is  jointed  at  D,  being  driven  by  a  tang  or 
tongue  on  one  piece  fitting  a  slot  in  the  other.  This  makes  a 
positive  drive  and  yet  does  away  with  any  spring  due  to 
heating,  as  each  piece  is  free  to  take  its  own  position  in  its 
own  bearing.  The  driving  spindle  is  H,  while  /  is  the  inner 
bearing,  the  outer  bearing  being  at  the  end  of  the  spindle 
and  slightly  tapered  on  the  outside  to  allow  taking  up  for 
wear. 

In.  the  lower  figure  we  have  the  supported  spindle  of 
the  same  grinder  driven  by  pulley  C,  in  bearings  B  which 


SOME    EXAMPLES    OF    DRAWINGS 


35 


l-tr1 


36  MACHINE    SHOP    DRAWINGS 

are  supported  from  the  double  cross  slides  A  A.  The 
main  spindle  has  a  cross  slot  for  driving  the  tang  of  the 
second  spindle  E,  which  in  turn  drives  the  third  and  grind- 
ing spindle  in  the  same  way.  This  is  to  avoid  heating  due  to 
any  slight  bending  of  such  a  long  spindle.  The  last  spindle 
carries  a  large  collar  and  has  a  threaded  projection  H  on 
which  the  wheel  bushing  or  arbor  is  screwed.  This  may 
carry  one,  two  or  three  wheels,  but  in  any  case  has  a  projec- 
tion on  the  end  which  fits  into  the  supporting  spindle  /. 
This  is  supported  in  a  sleeve  or  bushing  K,  very  similar  to 
the  one  on  the  other  end  and  serving  a  similar  purpose,  the 
support  of  the  wheels  against  the  work  in  grinding.  By 
driving  this  supporting  spindle  as  well  as  the  other,  and  at 
the  same  speed,  there  is  no  wear  on  the  small  projecting  end, 
all  wear  being  transferred  to  the  bearing  surfaces  which  are 
as  large  as  these  of  the  grinding  end.  The  upper  view 
gives  a  little  more  detail  of  this  construction. 

A  Boiler  Setting 

The  leading  dimensions  of  a  boiler  setting  for  a  48-inch 
return  tubular  boiler  is  shown  in  Fig.  21.  No  length  is 
given  as  this  can  vary  according  to  the  length  of  the  boiler, 
but  the  other  proportions  should  be  maintained  as  shown. 
The  grate  is  24  inches  below  the  boiler  and  is  4  feet  6 
inches  long.  The  bridge  is  a  long  table  instead  of  only  a 
deflecting  wall  as  is  often  used,  and  the  length  of  this  will 
vary  with  the  boiler.  There  is  15  inches  between  the  top 
of  this  and  the  boiler,  the  boiler  itself  being  43  inches  from 
the  floor  line.  There  are  18  inches  clearance  between  the 
end  of  the  boiler  and  the  back  wall,  with  a  curved  arch  to 
carry  the  heat  to  the  tubes.  The  dotted  line  shows  the 


SOME    EXAMPLES    OF    DRAWINGS 


37 


-Q-O— 0~0— 0--0-Vo~5"o"'o" 


F 


in 


3 8  MACHINE   SHOP   DRAWINGS 

accumulation  of  ashes  and  dust  that  can  be  expected  over 
the  bridge  and  in  the  cleaning  chamber  in  front. 


Details  of  a  Back  Rest  for  Ratchet  Drill. 

A  somewhat  unusual  but  very  plain  drawing  is  shown 
in  Fig.  22  which  shows  all  the  details  as  well  as  the  assembly 
of  a  back  rest  or  "old  man"  for  a  ratchet  drill.  Beginning 
at  the  upper  left-hand  corner  we  find  three  views  of  the  cast- 
iron  base  A,  which  show  the  front,  side  and  top  view. 
These  show  it  to  be  practically  an  angle  plate  with  a  lug 
or  boss  to  hold  the  upright  rod  B,  which  screws  into  it. 
The  rod  B  is  shown  below  it  and,  though  broken,  is  to  be 
1 8  inches  long,  exclusive  of  the  thread.  This  is  of  cold- 
rolled  steel. 

The  lever  arm  C  is  of  machine  steel,  round  at  the  end  and 
bored  to  fit  the  rod  B,  but  of  flat  section  with  the  depth  ver- 
tically to  resist  the  thrust  of  the  drill.  This  is  held  in 
position  on  the  rod  B  by  the  ring  clamp  or  binding  screw 
7  which  fits  around  the  rod  B  in  between  the  two  positions 
of  the  bored  end  of  C.  Around  this  goes  the  screw  block  D, 
with  the  washer  E  between  it  and  the  binding  handle  F, 
which  is  threaded  to  fit  the  threaded  portion  of  7.  Tighten- 
ing F,  forces  the  block  D  against  the  ends  of  C,  and  pulls 
the  clamp  ring  7  against  the  other  side  of  the  rod,  so  that 
it  is  bound  at  three  points  and  held  firmly. 

To  guide  and  support  the  upper  end  of  the  ratchet  drill 
is  the  screw  H,  held  in  the  screw  holder  G,  three  views  being 
shown.  This  shows  how  the  screw  holder  slips  on  the  flat 
bar  C,  how  it  is  held  in  place  by  the  small  screw  /  bearing 
against  C  and  how  it  is  tapped  on  the  other  side  for  the 


SOME    EXAMPLES    OF   DRAWINGS 


39 


40  MACHINE  SHOP  DRAWINGS 

pressure  screw  H.    And  finally  the  pressure  screw  itself, 
H,  of  which  only  one  view  is  needed. 

The  assembly  drawing  shows  everything  in  place,  easily 
distinguished  by  letters  although  these  are  hardly  necessary. 
While  this  is  a  very  simple  case,  almost  any  drawing  can 


FIG.  230.  —  Section  of  Cylinder. 

be  studied  out  in  the  same  way  if  we  go  at  it  easily  and  do 
not  get  excited. 

A  Locomotive  Cylinder 

The  drawing  shown  in  Fig.  23  a  and  b  is  made  from  a 
working  drawing  of  the  Baldwin  Locomotive  Works  and  gives 


SOME    EXAMPLES    OF    DRAWINGS 


some  idea  of  the  many  details  that  go  to  make  up  a  cylinder 
and  half  saddle  for  a  locomotive,  in  this  case  for  the  Central 
Railway  of  Brazil.  Many  of  the  minor  dimensions  have 


1 

Steim  Inlet 

1 

Steam  Port 

1 

Exhaust 

I 

1 

Ste«m  Port 

| 

1 

Steam  Inlet 

1 

FIG.  236.  —  Showing  Section  Parts. 

been  omitted  as  being  unnecessary  for  our  purpose,  but 
enough  have  been  left  to  show  the  general  proportions 
and  the  way  in  which  it  is  made. 

The  inside  diameter  of  the  cylinder  is  21   inches,  the 
outside  is  24  inches  and  the  inside  length  32!  inches,  which 


42  MACHINE    SHOP    DRAWINGS 

means  a  24-inch  stroke,  after  allowing  for  the  thickness  of  the 
piston  head  and  the  clearance.  Steam  from  the  boiler  comes 
down  through  the  steam  passage  55  and,  as  can  be  seen  by 
the  dotted  lines,  divides  and  goes  around  the  exhaust  passage 
EE.  This  can  be  seen  both  from  the  view  of  the  valve  seat 
which  has  been  drawn  over  the  cylinder  and  also  from  the 
other  view.  On  dividing,  the  steam  comes  into  the  steam 
chest  through  the  passages  marked  57  and  steam  inlet,  in 
the  two  views.  From  here  the  steam  admits  it  to  the  cylin- 
der through  the  long  passages  and,  after  it  has  done  its 
work,  the  exhaust  steam  finds  its  way  out  the  same  long 
crooked  ports  and  goes  out  the  stack  through  the  central 
passage  marked  E  and  exhaust.  The  shape  of  the  steam 
pipe  joint  is  shown  above  the  passage  and  at  right  angles 
to  its  face. 

The  frame  goes  each  side  of  the  saddle  casting  as  can  be 
seen  at  F  and  is  secured  by  bolts  running  in  both  direc- 
tions as  shown.  The  center  of  the  frame  is  25^  inches  from 
the  center  of  the  engine  and  the  cylinder  center  20^  inches 
beyond  this,  while  the  outside  of  the  cylinder  is  12$  inches 
from  the  center. 

This  is  a  patternmaker's  drawing  as  it  shows  the  dimen- 
sions of  the  curves  of  the  steam  and  exhaust  passages,  and 
the  machinist  would  have  no  use  for  these  as  they  are  not 
finished.  The  location  of  the  various  centers  is  shown 
and  also  the  length  of  the  different  distances  to  be  taken  in 
the  dividers  in  striking  these  curves. 

The  dotted  lines  outside  the  cylinder  show  ribs  for 
assistance  in  lagging  and  in  making  air  spaces  under  it. 
The  widths  of  steam  and  exhaust  ports  are  shown.  This 
also  shows  the  width  of  the  exhaust  passage  to  be  6  inches, 


SOME    EXAMPLES    OF    DRAWINGS  43 

with  the  walls  i  inch  thick.  It  also  shows  how  the  steam 
passage  divides  around  it  and  conies  up  on  each  side.  Vari- 
ous other  details  can  be  seen  by  looking  over  the  drawings 
carefully. 

Eccentric  and  Eccentric  Strap 

Two  other  parts  of  those  same  Brazilian  engines  are  shown 
in  Fig.  24,  and  aside  from  showing  all  the  dimensions  it 
also  shows  how  the  directions  for  working  are  given  in 
actual  practice.  For  example :  "  Cast  iron,  four  a  set,"  means 
that  the  material  is  cast  iron  and  that  four  pieces,  or  four 
eccentrics,  are  needed  on  each  engine.  "No  holes  in  out- 
side for  set  screw"  shows  that  the  set-screw  holes  must  be 
drilled  and  tapped  at  an  angle  sufficient  to  clear  the  outside 
or  rim,  or  else  some  device  used  which  will  drill  them  from 
the  inside.  The  set  screw  is  given  as  a  f-inch  screw  with 
square  head.  Nothing  is  said  about  the  threads  per  inch 
as  this  is  to  be  standard  in  all  cases  unless  otherwise 
stated,  which  means  9  threads  to  the  inch. 

The  eccentric  is  in  two  parts,  divided  on  the  center  line 
of  the  axle,  and  held  together  by  the  studs  shown.  Although 
the  drawing  does  not  show  any  threads  on  these,  we  know 
there  must  be  to  allow  the  keys  to  be  used  across  the  top, 
and  in  the  detail  of  this  stud  we  find  the  thread  to  be  if 
inches  long  on  a  i^-inch  stud,  while  the  hole  for  the  key  is 
^f  wide  and  i|  inches  long.  The  split  key  is  made  of  two 
pieces  of  sheet  steel,  each  a  T3^  piece  of  steel  fastened 
together  with  a  rivet  at  the  head.  The  points  are  opened 
out  after  they  are  in  place  to  prevent  their  backing  out. 

As  can  be  seen  the  axle  is  g£  inches,  the  key  ij  inches 
wide,  and  the  radius  of  the  outer  curve  around  the  axle 


44 


MACHINE   SHOP    DRAWINGS 

Eccentric  Strap  No.  1592 


Vic.  24.  —  Eccentric  and  Eccentric  Strap. 


SOME    EXAMPLES    OF    DRAWINGS  45 

5j  inches.  The  total  width  is  4  inches,  while  the  face  is 
3^  with  the  edges  turned  down  for  the  side  bearings  of  the 
eccentric  straps  shown  above. 

The  different  diameters  of  the  eccentric  strap,  where  it 
fits  the  eccentric,  is  clearly  shown  as  well  as  the  various 
curves.  The  extension  that  fits  the  eccentric  rod  is  tapered 
as  shown  and  the  taper  is  met  by  a  6-inch  radius  curve 
coming  from  the  outside  of  the  strap.  The  rod  is  flat  and 
fits  into  a  pocket,  shown  more  clearly  in  the  end  view  and 
extending  about  half-way  down  into  the  projection. 

The  oil  pocket  at  the  top  is  drilled  down  into  the  eccentric 
strap  and  from  here  to  the  eccentric  bearing.  At  the  side  is 
another  reservoir,  cast  into  the  strap  and  closed  by  the 
screwed  plug,  i  \  inch  in  diameter  and  a  14  thread,  a  special 
tap  for  such  places.  The  two  halves  of  the  strap  are  held 
together  around  the  eccentric  by  the  two  |-inch  bolts, 
double  nutted  and  having  a  pin  outside  the  outer  nut.  In 
this  case,  as  with  the  eccentrics,  it  takes  4  to  make  a  set 
and  it  is  so  marked  on  the  drawing. 

A  Chuck  Screw  Drawing 

Another  example  from  actual  practice  is  the  chuck  screw 
from  the  Carter  Chuck  Company  as  seen  in  Fig.  25. 

This  shows  at  a  glance  that  the  finished  length  of  the 
screw  must  be  5^  inches  and  the  largest  diameter  f  inch, 
so  we  would  take  an  inch  bar  and  cut  it  off  accordingly. 
The  small  end  is  |£  inch  in  diameter  and  is  straight  on  the 
outside,  but  the  thread  is  cut  on  a  taper  of  i  inch  per  foot, 
as  shown  by  the  note.  The  thread  is  n  per  inch,  United 
States  standard  form  and  .57  inch  in  diameter  at  the  bottom. 

The  large  end  of  the  taper  under  the  thread  is  .663  and 


46  MACHINE   SHOP   DRAWINGS 

from  here  it  is  turned  straight  for  a  distance  of  ij  inches. 
The  thread  on  the  large  portion  is  also  1 1  to  the  inch  but  is 
of  the  Acme  standard  form.  Both  threads  are  right-handed. 
This  threaded  portion  is  2§  inches  long  and  adding  up  the 


FIG.  25.  —  A  Peculiar  Chuck  Screw. 


three  lengths  we  see  they  tally  with  the  total  dimension 
given.  The  bottom  of  the  thread  is  .764  inch,  the  slot  in 
the  end  is  J  inch  wide  and  ^  inch  deep,  giving  us  all  dimen- 
sions needed  to  cut  this  screw  from  the  solid  bar. 


( -4X--  1 


r 


FIG.  26.  —  The  Outside  Screw. 


The  Outside  or  Main  Screw 

This  is  shown  in  section  in  Fig.  26.  The  outside  dimen- 
sions are  if  by  4!  inches  long  with  a  square  thread,  cut 
5  to  the  inch  on  the  outside  over  the  whole  length,  and  an 


SOME    EXAMPLES    OF    DRAWINGS  47 

internal  thread  of  the  Acme  form  cut  n  to  the  inch  and  3! 
inches  long  with  a  diameter  of  .895  outside  or  just  .02  inch 
larger  than  the  screw  in  Fig.  25  which  fits  inside  of  it, 
giving  a  play  of  one  one-hundreth  of  an  inch  on  each  side 
of  the  screw. 

At  the  end  of  the  internal  screw  is  a  chamber  or  recess 
of  the  same  diameter  as  the  outside  of  the  thread,  for 
allowing  the  chasing  tool  or  tap  to  run  into.  This  recess  is 
|  inch  long.  Leading  into  this  from  the  other  end  of  the 
screw  is  the  hole  which  the  end  view  proves  to  be  square 
with  slightly  rounded  corners.  This  is  -^  inch  square  on  the 
sides  and  had  fillets  or  corners  of  -^  inch  radius.  This 
shows  us  that  this  screw  fits  on  the  outside  of  the  inner 
screw  or  stud  shown  in  Fig.  25,  and  that  this  is  turnecl  by  a 
wrench  having  a  square  end  which  fits  into  the  square  hole 
shown  in  the  end. 

Detail  Drawing  of  a  Special  Flange 
A  very  good  example  of  a  detail  drawing  giving  very  close 
limits  is  shown  in  Fig.  27.  The  drawing  is  used  in  connec- 
tion with  a  table  as  the  most  of  the  dimensions  are  repre- 
sented by  letter.  Beginning  with  the  12  small  holes  on  the 
inside  of  the  flange  we  find  these  are  to  be  drilled  and  tapped 
for  a  No.  8-32  tap,  meaning  a  No.  8  machine  screw  size  with 
32  threads  per  inch.  There  are  6  sets  or  pairs  of  holes. 
The  next  row  of  holes,  six  in  number,  are  outside  of  these, 
tapped  to  the  same  size,  while  the  outer  holes  have  a  No.  14- 
20  tap  and  are  countersunk  —  this  being  shown  by  the 
letters  C.  S. 

Some  of  the  other  holes  are  shown  at  the  right.  One  with 
a  £f  drill,  f  inch  deep  and  tapped  with  a  f-inch  tap  having 


48 


MACHINE    SHOP    DRAWINGS 


3 
I 


•(•    Jaja1'!  1<  .'"JgTro^  g    n  !!' 

X  3      «.^-^        *    I  I  ^*"  :j.|i  "tff^Z O~  *  ~H  '   | 

if  ?!  i,- -      -^~ 
'i    '8  § 


SOME    EXAMPLES    OF    DRAWINGS  49 

a  standard  thread,  16  to  the  inch.  Then  there  are  4  holes, 
90  degrees  apart,  drilled  with  a  No.  23  drill  and  tapped 
with  a  No.  10-32  tap,  while  down  below  is  a  No.  8-32  tap, 
|  inch  deep. 

It  is  needless  to  follow  all  the  holes  and  we  will  now 
look  at  some  of  the  limits  imposed,  which  indicates,  although 
it  does  not  prove,  that  it  is  a  toolmaker's  job.  In  the  right- 
hand  piece  it  will  be  seen  the  half-inch  reamed  hole  must 
be  1.093  inches  from  the  center  line  within  a  thousandth  of 
an  inch,  meaning  that  it  can  be  either  1.092  or  1.094  or 
anything  in  between. 

In  the  center  drawing  everything  has  limits,  some  of 
them,  it  will  be  noticed,  only  containing  a  maximum  or 
minimum  limit,  but  not  both.  This  means  that,  in  the  case 
of  the  flange  thickness  for  example,  the  flange  can  be 
between  .499  and  .500,  but  not  over  the  larger  dimension 
given;  some,  on  the  other  hand,  have  minimum  limits 
given. 

This  also  shows  that  cross-sections  maybe  given  in  various 
ways.  The  center  view  is  a  clear,  straight  cross  cut  through 
the  center  on  the  line  AOB  of  the  left-hand  view.  In  the 
lower  view,  on  the  other  hand,  the  cross-section  is  not  a 
straight  line,  but  from  C  to  O  and  from  here  to  D.  This  is 
to  show  a  section  through  the  bolt  lug  D  and  at  the  same 
time  show  the  recess  at  the  right  which  is  |  inch  wide. 
The  small  view  gives  a  part  section  along  the  line  OE. 


CHAPTER   IV 


HINTS   ON   LAYING   OUT 


EVERY  machinist  needs  a  few  good  tools,  such  as  a  steel 
square,  bevel,  dividers,  calipers  and  protractor  to  measure 
angles,  but  he  can  do  more  laying  out  with  only  a  pair  of 
dividers,  a  straight  rule  and  a  scriber  than  many  imagine. 


FIGS.  28  and  29.  —  Finding  4  and  8  equal  points. 

It  is  better  to  have  but  few  tools  and  know  how  to  use  them 
than  to  have  a  whole  kit  full  and  not  understand  all  about 
them. 

Suppose  you  want  to  lay  out  some  templets  for  bolt 
holes  in  flanges  for  pipe  or  similar  work,  to  have  four, 
six  and  eight  holes  each.  All  you  need  are  the  dividers, 
scale  and  scriber. 

Draw  a  line  A  B,  Fig.  28,  take  any  point  for  the  center, 


HINTS    ON    LAYING    OUT  51 

and  draw  a  circle  for  the  outside  of  the  flange,  and  another 
circle  inside  this  for  the  location  of  bolt  holes  or  bolt  diam- 
eters, as  it  is  called.  Two  of  the  four  holes  will  be  where 
line  AB  cuts  the  circle  at  a  and  b.  Take  any  distance  in 
the  dividers,  more  than  half  of-AB,  and  draw  the  arcs 
shown  inside  the  circles,  using  a  and  b  as  centers,  so  as  to 
cross  at  two  points,  c  and  d.  Draw  a  line  that  will  cut  both 
c  and  d,  and  extend  this  to  the  circles,  cutting  them  at  e  and/. 
This  line  ef  will  be  at  exactly  right  angles  to  the  first  line, 
and  e  and  /  will  be  just  half-way  between  a  and  b.  Prove 
this  by  taking  the  distance  ae  in  your  dividers  and  trying  it, 
Always  prove  any  work  of  this  kind  to  be  sure  there  has 
been  no  slip.  This  will  always  give  you  two  lines  at  right 
angles  without  using  a  square  of  any  kind,  and  will  also 
divide  any  distance,  as  ab,  exactly  in  half. 

Locating  the  Half-way  Point 

To  lay  out  a  templet  with  eight  holes,  it  is  simply  neces- 

\       sary  to  locate  four  more  holes  half-way  between  the  holes 

|p   already  laid  out  in  Fig.  28.      This  can   be  done  by  the 

v  same  method  of  dividing  any  distance  in  two  equal  parts 

(see  Fig.  29).     With  one  leg  of  the  dividers  on  b,  and  any 

v  distance  more  than  half  the  distance  from  b  to/,  make  the 

^curves  shown.     With  the  same  setting  and  the  point  on/, 

^  make  another  curve,  cutting  the  first  in  c  and  d.     A  straight 

s;  line  through  these  two  points,  c  and  d,  will  show  the  point 

g  to  be  half-way  between  b  and/.     The  other  end  of  the 

—  line  will,  if  extended,  cut  the  other  side  of  the  circle  at  *  and 

r-1  give  half  the  distance  from  a  to  e.     Take  the  distance  bg 

or  gf  and,  with  dividers  on  /,  mark  h.     Prove  this  by  also 

"Busing  a  as  a  center  and  cutting ^e  first  mark  at  h.     Do  the 
Q_ 


CO 


STATE  NORMAL  SCHOOL 
UAt  AUTS  *Vf  HOME  ECOHOIWBS 
SANTA  BARRARA,  CALIFORNIA 


52  MACHINE   SHOP    DRAWINGS 

same  at  e  and  b,  which  will  locate  ;,  and  the  eight  holes 
are  all  laid  out.  Prove  them  all,  and  if  the  work  has  been 
carefully  done  they  will  be  laid  out  as  accurately  as  though 
you  had  used  very  elaborate  tools,  probably  more  accurately 
than  you  would  do  it  with  a  protractor  to  measure  the  angles. 

Radius  gives  One  Side  of  Hex 

To  lay  out  six  holes  requires  no  measurements  whatever 
for  the  distance,  as  the  radius  or  half  diameter  of  the  circle 


FIGS.  30  and  31.  —  Laying  out  a  Hexagon. 

is  the  right  setting  for  one  side  of  a  "hex"  or  hexagon,  as  a 
six-sided  figure  is  called  (see  Fig.  30).  With  the  same 
setting  used  in  drawing  the  circle,  place  one  leg  on  a  and 
step  around,  marking  b,  c,  d,  e,/one  after  the  other.  Prove 
this  by  going  around  the  other  way  and  cutting  the  first 
marks  as  shown.  Fig.  30  shows  the  marks  at  top  and 
bottom  and  Fig.  31  shows  them  at  the  side.  Sometimes 
the  plans  call  for  one,  sometimes  for  the  other. 

To  make  a  i2-holed  templet,  divide  the  distance  between 
the  holes  as  in  Fig.  29,  and  the  rest  is  easy. 


HINTS    ON    LAYING    OUT 


53 


Six,  Eight  and  Ten  Rule 

Fig.  32  shows  another  and  very  handy  way  of  laying  out 
a  right  angle  or  square  corner  with  only  the  dividers  and 
rule,  as  already  in  use.  This  is  one  of  the  handiest  things 
for  any  one  to  remember,  as  it  comes  into  play  whether  you 
are  laying  out  a  small  tool,  making  a  try  square  for  yourself, 
laying  out  a  tennis  court,  or  staking  out  for  a  house  founda- 
tion. It  is  called  the  "6,  8  and  10  rule"  and  dates  way  back 
to  the  ancient  Greeks,  but  it's  one  of  the  things  that  never 


b  a  b 

FIGS.  32  and  33.  —  Two  Ways  of  Laying  Out. 

get  old.  This  rule  or  law  is  that  any  triangle  whose  sides 
are  in  the  proportion  of  6,  8  and  10,  no  matter  whether  it 
is  inches,  feet  or  miles,  is  a  right  angle.  Take  in  your 
dividers  6  of  any  units  you  want  —  inches,  eighths  o^ 
sixteenths  —  and,  with  one  point  at  a,  scribe  an  arc  as  at  b. 
Then  take  8  of  the  same  units  and,  with  one  point  again  on 
a,  scribe  above  as  at  c.  Then  take  10  of  these  same  parts 
and,  with  one  point  on  either  arcs  b  or  c,  scribe  a  mark 
cutting  the  other  arc.  Draw  a  triangle  from  these  points 
as  at  a,  &  and  c,  and  you  have  a  right  angle  every  time.  If 
you  had  taken  the  point  e  instead  of  &,  with  the  10  units  in 


54 


MACHINE    SHOP    DRAWINGS 


the  dividers,  the  other  corner  would  be  at  d,  and  the  tri- 
angle as  shown  by  the  dotted  lines,  but  the  angle  is  90 
degrees,  or  exactly  a  right  angle. 

Triangular  Method 

Another  way  you  can  lay  off  a  square  corner  without 
measurements  of  any  kind  is  shown  in  Fig.  33.  With  the 
dividers  at  a  and  any  distance  in  the  dividers,  mark  from 
b  to  c.  Shift  the  point  to  b  and  draw  the  arc  ac.  Where 
these  cut  each  other,  in  c,  again  place  the  point,  with  the 
same  distance  as  before,  and  scribe  the  arc  b.  Then  take  a 
scale  and  draw  a  straight  line  from  b,  through  point  c,  and 
continue  to  d.  From  the  point  d  to  a,  draw  another  line 
ad,  and  this  will  be  at  exact  right  angles  to  ab. 

Using  this  as  a  start,  it  is  easy  to  lay  out  a  hexagon  as  the 
side  be  is  already  there  and  ab  extended  to  i  gives  the  base 
line.  Keep  the  distance  ab  in  the  dividers,  and  from  b 
mark  off  h.  From  this  point  mark  curve  ig.  From  *  draw 
curve  hg.  Draw  hg  and  you  have  three  sides  of  the  hexagon 
done,  cbhg.  Draw  straight  lines  through  ig  and  ac.  With 
dividers  on  c  and  g  draw  e  and  /;  connect  e  and  /  and  the 
hexagon  is  complete,  without  measuring  an  angle  of  any 
kind.  Prove  the  work  by  stepping  off  the  various  sides. 

Independent  of  Try  Squares 

From  these  two  methods  of  finding  a  square  corner  you 
will  see  that  even  if  all  the  squares  in  the  world  should  be 
suddenly  lost,  we  would  have  a  way  of  making  new  ones 
always  at  hand. 

Fig.  34  shows  this  same  method  applied  to  laying  out  a 
square.  The  side  will  be  ad.  Taking  this  in  your  dividers 


HINTS    ON    LAYING    OUT 


55 


and  with  the  point  on  a  mark  /.  From  /  scribe  at  e  and 
repeat  this  form  from  d.  Where  these  marks  cross,  gives 
the  corner  of  the  square  and  the  sides  can  be  drawn  as  is 
shown. 

In  Fig.  35  the  square  corner  is  found  by  the  dividing 
method  shown  in  Fig.  28  and  the  lines  of  and  de  are  laid  off 
at  right  angles  in  this  way.  With  dividers  at  o  mark  g  and 


FIGS.  34  and  35.  —  Other  Methods  of  Laying  Out. 

h.  Connecting  these  points  gives  a  45-degree  angle  and 
one  corner  of  an  octagon.  From  this  you  can  go  on  and 
lay  out  a  complete  eight-sided  figure  as  shown. 

If  you  want  to  make  it  of  some  particular  size,  lay  off 
one  side  of  the  desired  length  such  as  hi.  At  i,  draw  a  line 
at  right  angles  to  the  base  by  the  method  shown  in  dotted 
lines.  With  distances  hi  in  the  dividers  and  one  point 
at  i,  draw  the  half-circle  hf.  Divide  //  in  half  the  same  as 


MACHINE    SHOP    DRAWINGS 


in  Fig.  29,  and  draw  ik.  With  the  distance  hi  or  ik  (both 
the  same)  mark  off  kl,  Im  (where  it  cuts  the  dotted  line 
marks  one  corner),  mn  and  so  on  around  the  figure. 

Fig.  36  shows  another  application  of  the  first  principle 
in  dividing  up  a  square  or  any  figure  with  square  corners 
into  equal  parts.  This  idea  can  be  applied  in  many  ways 
and  is  a  good  thing  to  remember,  as  well  as  the  other  two 
ways  of  finding  a  square  corner  shown  in  Figs.  32  and  33. 
They  are  very  handy  in  many  kinds  of  work. 


FIG.  36.  —  Dividing  the  Sides  of  any  Figure. 

Square  Corner  Without  Dividers 

There  is  also  a  very  neat  way  of  laying  out  a  square 
corner  without  dividers,  and  even  the  scale  can  be  dispensed 
with  if  you  have  a  straight-edge  to  draw  by. 

Suppose  you  want  to  make  a  square  corner  at  A,  Fig.  37. 
Take  any  distance  as  AC  and  draw  it  any  old  way;  this 
happens  to  be  nearly  45  degrees.  Mark  the  same  distance 
each  side  of  C,  in  a  straight  line  as  DCB.  Join  BA  and 
AD,  and  the  corner  A  is  exactly  square. 


HINTS    ON    LAYING    OUT 


57 


The  same  thing  is  shown  in  Fig.  38,  but  with  the  first 
line  EG  at  a  very  different  angle.  HG  and  GF  equal  EG, 
and  joining  FE  and  EH  completes  the  corner.  This  can 
be  done  with  dividers  in  the  same  way,  but  shows  that  when 
you  have  or  can  get  a  straight-edge  of  any  kind  you  can 
make  a  square  corner  while  you  would  be  hunting  up  the 
regular  tools. 

The  best  way  to  see  all  the  workings  of  these  methods 
is  to  take  a  sheet  of  metal  of  some  kind  —  tin,  brass,  copper, 


FIGS.  37  and  38. 

or  iron  —  and  lay  them  out  to  a  good  scale.  With  the  6,  8, 
and  10  rule  take  3,  4  and  5  inches,  or  12,  16  and  20  inches, 
according  to  the  size  sheet  you  are  working  on.  If  you  get 
these  principles  down  fine  you  will  never  be  stuck  on  an 
outside  job  because  you  have  forgotten  your  square,  and 
it  is  mighty  handy  to  know  even  in  laying  out  jig  and  similar 
work,  right  in  the  shop  itself. 

Something  About  Angles 

Angles  play  an  important  part  in  mechanical  drawing, 
as  we  shall  see.  Suppose  we  look  at  the  end  of  a  square 
bar,  as  in  Fig.  39,  and  we  have  no  means  of  knowing  whether 


58  MACHINE    SHOP    DRAWINGS 

the  end  is  square  across  the  bar,  or  is  flat  or  rounded,  as  the 
bounding  lines  will  be  the  same  in  any  case.  It  takes  a 
side  view  to  show  whether  the  end  is  slanting,  as  in  B, 
this  being  an  angular  view,  or  of  any  other  shape,  as  in  C 
above.  The  top  view  would  be  as  in  D. 

This  brings  us  to  what  is  called  projection,  or  the  throw- 
ing out  of  lines  to  show  what  shape  a  piece  really  is  or 
what  it  looks  like  in  different  views. 


FIG.  39 

Having  a  bar  4  inches  square  we  cut  the  end  at  an  angle 
that  makes  the  short  side  of  the  bar  3  inches  shorter  than 
the  other,  as  shown  in  Fig.  40.  The  end  or  top  view  is 
square,  but  as  we  look  horizontally  at  the  slanting"  side  it 
appears  as  a  rectangle  3X4  inches,  as  at  A,  while  if  we  look 
square  at  the  angular  surface  it  is  4  X  5  inches,  as  shown 
in  the  angular  projection  B.  The  side  view  is  at  C. 

Fig.  41  shows  the  effect  of  a  triangular  bar  being  cut  at 
an  angle.  The  change  in  the  shape  is  shown  by  comparing 


HINTS    ON    LAYING    OUT 


59 


the  true  section  or  end  view  B  with  the  angular  view  A, 
which  is  an  elongated  triangle.     This  is  at  right  angles  to 


FIG.  41 


the  angular  surface.     The  side  view  C  does  not  show 
whether  the  bar  is  round,  square  or  triangular. 


6o 


MACHINE    SHOP    DRAWINGS 


Curved  Surfaces 

Bodies  with  flat  sides  or  surfaces  are  comparatively  easy 
to  throw  in  any  sort  of  projection,  but  when  it  comes  to 
curved  surfaces  it  is  a  different  matter.  Take  a  round 
stick  and  cut  the  end  at  a  slight  bevel.  Look  at  it  square 
with  the  cut  and  see  that  it  is  not  round  but  elliptical;  look 


FIG.  42 

at  it  sideways  and  see  that  this  also  shows  an  ellipse,  but 
with  the  long  axis  the  other  way.  Cut  it  at  different  angles 
and  note  how  the  ellipses  change  shape  with  each  angle. 

In  mechanical  drawing  it  is  necessary  to  know  how  to 
draw  these  ellipses  both  to  show  how  they  will  look  and 
for  the  purpose  of  laying  out  sheet  metal  to  fit  such  a  shape, 
either  for  an  angular  cover  or  for  a  stove-pipe  elbow. 


HINTS    ON    LAYING    OUT 


61 


In  Fig.  42  the  side  view  does  not  give  any  idea  as  to  its 
shape.  But  when  we  project  the  lines  a  and  b  from  the 
top  and  bottom  of  the  slanting  side,  we  find  that  the  angular 
end  looks  like  an  ellipse  if  we  look  at  it  in  the  center  and  in 
the  direction  of  the  arrow.  The  top  view  will,  of  course,  be 
round  as  in  B. 


FIG.  43 

Fig.  43  shows  a  round  bar  cut  at  a  more  acute  angle,  and 
two  projections  are  made  to  show  how  it  appears  when 
looked  at  from  two  views:  either  square  with  the  cut  or 
square  with  the  side  of  the  bar.  Then  diameter  A  remains 
the  same  in  all  cases,  but  the  long  diameter  of  the  ellipse  is 
decidedly  different,  as  can  be  seen. 


62  MACHINE    SHOP    DRAWINGS 

Laying  Out  Sheet  Metal 

If  it  was  necessary  to  cut  a  sheet  of  metal  to  fit  the  end 
of  a  bar  cut  at  an  angle  it  might  be  puzzling  unless  we  could 
put  the  piece  over  the  bar  and  mark  around  it.  But  there 
is  a  way  of  laying  out  all  such  shapes  without  marking 
around  the  bar,  and  it  is  a  very  handy  thing  to  know. 

Suppose  we  want  to  make  a  funnel  like  Fig.  44,  how  will 
we  cut  out  the  sheets  so  as  to  form  the  right  shape  when 
rolled  up  ?  This  is  really  two  partial  cones  joined  together, 
and  in  laying  them  out  we  consider  them  as  complete  cones 
so  as  to  get  a  center  or  starting-point.  We  can  do  this  either 
by  drawing  down  the  sides  until  they  meet  as  at  a,  or  we 
can  figure  it  out  in  the  same  way  we  do  tapers.  The  large 
cone  tapers  from  7  inches  to  2  inches  in  a  distance  of  5 
inches,  or  a  taper  of  5  inches  in  5  inches  or  i  inch  to  each 
inch.  So  we  know  that  the  point  a  is  7  inches  from  the 
top,  as  shown. 

Next  we  figure  out  the  distance  around  the  funnel  at 
each  end  by  multiplying  both  7  and  2  by  3},  or  3.1416, 
which  gives  22  inches  around  the  top  and  6.28  inches 
around  the  bottom.  So,  taking  a  point  as  b,  Fig.  46,  with 
2  inches  in  the  compass  or  dividers  if  it  is  done  on  metal, 
draw  part  of  a  circle.  Then  with  a  7-inch  radius  draw 
another  part  of  a  circle.  Take  the  dividers  and  step  off 
22  inches  on  the  large  circle,  preferably  half  on  each  side 
of  a  center  line,  and  connect  the  points  and  the  center  by  a 
line  at  each  end  of  the  curved  piece.  As  these  lines  must 
be  radial  from  the  center,  it  is  only  necessary  to  step  off 
the  distance  on  one  circle,  and  the  larger  one  is  best  as  there 
is  less  chance  of  error.  This  curved  sheet  when  rolled 


HINTS   ON   LAYING   OUT 


PIG.  44 


FIG.  45 


FIG.  46 

Laying  Out  Curved  Surfaces. 


64  MACHINE    SHOP    DRAWINGS 

up  will  make  the  upper  part  of  the  funnel,  as  can  be  tried 
with  a  piece  of  paper.  As  no  allowance  has  been  made 
for  the  lapping  we  will  add  a  piece  on  one  end,  shown  by 
dotted  lines,  which  gives  room  for  riveting  or  soldering. 
The  same  process  repeated  for  the  lower  end  of  the  funnel 
is  shown  in  Fig.  45  and  needs  no  further  explanation. 

What  an  Elbow  Looks  Like 

The  left  view  of  Fig.  47  shows  the  side  of  an  elbow,  the 
angle  being  as  indicated.  How  shall  we  lay  out  a  sheet  that 
will  make  an  elbow  of  this  angle? 

The  laying  out  is  an  easy  matter  if  we  follow  each  step 
in  the  program.  First,  find  the  width  of  the  sheet  by  mul- 
tiplying the  diameter  by  3},  or  3.1416.  This  is  from  A 
to  B.  Draw  a  half-circle  on  the  pipe  diameter,  as  shown, 
and  divide  this  into  any  number  of  equal  parts;  the  larger 
the  scale  and  the  greater  the  number  of  divisions  the  more 
accurate  the  layout  will  be.  In  this  case  there  are  10  divi- 
sions, and  the  circle  could  just  as  well  be  above  the  line 
as  below,  anywhere  to  get  a  curve  the  same  as  the  shape 
of  the  body  of  the  piece  for  laying  out  the  divisions. 

From  each  point  on  the  circle  draw  lines  vertically  to  the 
angular  line  as  i-i,  2-2,  etc.  Divide  half  the  length  of  AB 
into  the  same  number  of  equal  parts,  as  shown  by  i,  2,  3, 
etc.,  and  project  the  lines  down  to  the  lower  line  of  the 
angle.  Draw  lines  horizontally  from  the  angular  line  to 
these  vertical  lines  and  make  the  points  as  a,  b,  c,  etc. 
Connect  these  by  an  easy  curve,  as  shown.  This  is  half 
the  elbow,  and  the  other  side  is  just  the  same.  Allow  the 
space  for  riveting,  as  shown  by  the  dotted  lines  at  B,  and 
the  elbow  sheet  is  laid  out.  If  the  seam  is  wanted  on  the 


HINTS    ON    LAYING    OUT 


66  MACHINE    SHOP    DRAWINGS 

long  side  or  at  any  other  point,  we  need  only  to  begin  the 
layout  at  that  point. 

A  Side  Outlet 

In  Fig.  48  we  have  a  pipe  1 2  inches  in  diameter  with  a 
side  outlet  10  inches  in  diameter.  The  shape  of  the  end 
of  this  outlet  to  fit  the  large  pipe  is  not  easy  unless  we  lay 
it  out  in  the  same  way  as  the  elbow.  Here  it  fits  on  a  curved 
surface  so  that  both  the  curve  of  the  piece  itself  and  of  the 
large  pipe  must  be  considered.  Draw  the  pipe  in  position 
as  at  the  left,  to  show  its  size  and  hight.  Figure  out  the 
length  around  it  as  in  the  other  case  and  we  have  10  X 
3.1416=  31.416  inches.  AB  is  one-half  of  this,  as  we 
have  laid  out  only  half  the  piece.  Draw  the  half-circle  to 
the  lo-inch  diameter,  either  below,  as  shown,  or  above  the 
side  outlet,  and  divide  this  into  as  many  parts  as  seems 
necessary.  In  this  case  there  are  six  divisions  to  the 
quarter-circle.  Project  the  lines  upward  to  the  large  circle. 
Divide  the  long  strip  into  the  same  number  of  parts  and 
project  lines  at  right  angles  to  cut  these,  as  the  points  i,  2, 3, 
4,  5,  etc.  Through  these  draw  an  easy  curve,  as  shown, 
which  gives  the  outline  necessary  to  fit  against  the  larger  pipe 
in  this  case. 

Information  About  the  Screw  Thread  or  Helix 
We  sometimes  see  screw  threads  drawn  with  the  curved 
lines  as  they  appear  when  you  look  at  a  screw  that  has  a 
fast  pitch  for  a  small  diameter.  In  actual  drawing  for 
practical  purposes  we  do  not  even  draw  the  threads,  only 
a  few  lines  to  indicate  where  they  are,  but  it  is  interesting 
to  know  how  the  other  is  done.  The  plan  is  much  the  same, 


HINTS    ON    LAYING    OUT 


67 


as  we  shall  see,  and,  having  fixed  the  principle  of  the  thing 
in  your  mind  it  can  be  applied  to  any  form  of  laying  out 
that  is  necessary. 


FIG.  49.  —  Method  of  Laying  Out  a  Screw  Thread. 
Taking  the  outside  of  the  screw  first,  we  draw  the  larger 
half-circle,  as  in  Fig.  49,  and  divide  into  six  parts.  Then 
lay  out  the  pitch  down  the  sides  and  divide  this  into  the 
same  number  of  parts,  drawing  lines  straight  across  the 
body  of  the  screw  as  0-6,  1-5,  2-4,  etc. 


68  MACHINE    SHOP    DRAWINGS 

Draw  lines  down  from  the  divisions  on  the  half-circle, 
cutting  the  cross-lines,  and  lay  off  the  intersections  as  a,  b, 
c,  d  and  e.  Joining  these,  give  the  curve  for  the  outside  of 
the  screw,  which  is  not  very  pronounced.  When  it  comes 
to  the  bottom  of  the  thread  we  have  an  example  of  a  fast 
pitch  on  a  small  diameter,  for,  while  the  pitch  is  the  same, 
the  diameter  is  much  less.  In  this  case  we  draw  the  smaller 
half-circle,  representing  the  bottom  of  the  thread,  and  divide 
this  in  just  the  same  way.  Marking  off  these  intersections 
we  get  the  much  more  pronounced  curve  shown. 

The  upper  part  of  this  shows  a  F-thread,  while  the  lower 
part  shows  a  square  thread.  The  intersections  of  the  dif- 
ferent points  are  shown  by  the  small  crosses.  These  show 
plainly  how  the  thread  angles  change  for  each  diameter 
and  pitch  and  why  the  side  clearance  on  thread  tools  is 
such  an  important  matter.  By  keeping  in  mind  the  reasons 
for  all  these  different  laying-out  or  intersection  points,  any 
work  of  this  kind  can  be  handled  without  difficulty,  and  it 
often  comes  in  very  handy  to  know  about  it. 

Curves  Cut  by  an  End  Mill 

Laying  out  in  this  way  can  also  be  used  to  show  the  curve 
that  will  be  cut  by  an  end  mill  if  it  is  tipped  from  the  ver- 
tical position.  This  can  be  laid  out  in  exactly  the  same  way 
as  the  curves  for  the  elbows  and  other  sheet  metal  work. 
When  in  a  vertical  position  a  flat  surface  will  be  cut  as  at 
A,  Fig.  50,  while  by  inclining  the  spindle  to  the  work  as  at  B 
and  C  the  curves  shown  will  be  cut  in  the  metal  moved 
across  the  face  of  the  cutter.  There  are  many  times  when 
this  can  be  used  to  advantage  in  tool  making  and  other 
work. 


HINTS    ON    LAYING    OUT 


69 


Laying  Out  Any  Angle  You  Need 
It  sometimes  happens  that  you  want  to  lay  out  some 
particular  angle  and  that  no  protractor  is  handy.     You 
can  get  almost  any  angle  you  want  and  with  a  good  degree 


FIG.  50.  —  Curves  Secured  with  one  End  Mill. 

of  accuracy  if  care  is  used  and  you  know  how  to  go  about 
it.  Draw  a  straight  line,  Fig.  51,  as  a  base,  and  taking  any 
size  in  the  dividers,  draw  the  arcs  shown,  and  by  connecting 
points  a  b  and  c  we  have  a  6o-degree  angle. 

Dividing  the  distance  be  by  the  well-known   method  of 


7o 


MACHINE    SHOP    DRAWINGS 


taking  more  than  half  the  distance  in  the  dividers  and 
drawing  an  arc  from  each  point  so  that  they  will  cross,  then 
drawing  a  line  through  the  intersections  and  we  have  d,  so 
we  know  cd  or  db  is  30  degrees  or  half  of  cb. 

Dividing  db  in  the  same  way,  always  working  along  the 
arc  and  not  on  the  straight  lines,  we  get  de  or  eb  and  know 
they  must  be  15  degrees  each.  This  can  be  carried  on 
until  you  get  to  degrees,  dividing  15  into  three  equal  parts 
by  stepping  off  carefully  with  the  dividers.  This  gives  5 
degrees  and  these  can  be  divided  on  down  to  the  single 
degree. 


FIGS.  51  and  52.  —  Dividing  to  Get  any  Degree  you  Want. 

Fig.  52  shows  a  quarter-circle  divided  up,  as  can  be  done 
with  the  divider  alone  and  without  a  protractor  or  triangle 
of  any  kind.  The  90  degrees  are  divided  into  three  30- 
degree  angles,  irfto  a  45, 15  and  six  5-degree  angles,  making 
90  in  all,  of  course,  and  -one  of  these  5-degree  spaces  is  di- 
vided into  five  making  single  degrees. 

Suppose  you  want  an  angle  of  57  degrees  or  3  degrees  less 
than  60.  You  have  only  to  lay  out  the  60  degrees  as  we  did 
at  first,  then  take  away  3  degrees  as  found  by  dividing  one  of 
the  5-degree  spaces  into  single  degrees.  In  this  way  it  is  easy 


HINTS    ON   LAYING    OUT  71 

to  get  any  number  of  degrees  wanted,  or  the  table  on  page  72 
may  be  found  handy  if  it  is  remembered  that  the  distances 
are  given  for  a  i-inch  radius  as  shown  in  Fig.  53.  To  use 
it,  draw  part  of  a  circle  in  some  even  inches  from  a  base  line 
and  lay  off  from  b  to  c  the  distance  shown  in  the  table,  mul- 
tiplied by  the  number  of  inches  of  radius  used.  That  is, 
if  you  have  4  inches  in  the  dividers  in  drawing  the  circle, 
multiply  the  value  by  4.  For  accurate  laying  out  it  is  a  good 
plan  to  use  10  inches  and  multiply  all  the  values  by  10. 


FIG.  53.  —  Laying  Out  from  a  Table. 

By  doing  this  the  error  is  very  much  less  than  in  attempt- 
ing to  measure  on  a  radius  of  i  inch.  To  lay  off  an  angle 
of  24  degrees,  find  in  the  table  .4158,  which  means  that  with 
the  distance  ab  i  inch  and  the  distance  be  .4158,  the  angle 
will  be  24  degrees.  Or  with  a  xo-inch  radius  ab,  the  dis- 
tance be  will  be  4.158  inches  for  a  24-degree  angle. 

In  the  same  way  we  can  find  any  angle  by  laying  it  off 
on  metal  or  paper  and  measuring  the  distance,  be,  from  the 
table. 


MACHINE    SHOP    DRAWINGS 


TABLE  OF  CHORDS  FOR  FINDING  DEGREES  AT  I-!NCH  RADIUS 


I 

.0174 

24 

.4158 

46 

•78i5 

69 

•  1328 

2 

.0349 

25 

•4329 

47 

•7975 

70 

.1471 

3 
4 

53 

26 
27 

•4499 
.4669 

48 
49 

•8135 
•8294 

7' 
72 

.1614 
.1756' 

5 

.0872 

28 

.4838 

5° 

•8452 

73 

.1896 

6 

•  1047 

29 

.5008 

5i 

.8610 

74 

.2036 

7 

.1221 

3° 

.5176 

52 

.8767 

75 

•2175 

8 

•1395 

3i 

•5345 

53 

.8924 

76 

•2313 

9 

•1569 

32 

•5513 

54 

.9080 

77 

•  245° 

10 

•1743 

33 

.5680 

55 

•9235 

78 

.2586 

ii 

.1917 

34 

.5847 

56 

•9389 

79 

.2721 

12 

.2O90 

35 

.6014 

57 

•9543 

80 

.2856 

13 

.2264 

36 

.6180 

58 

.9696 

81 

.2989 

14 

11 

•2437 
.26lO 

.2783 

ii 

39 

.6346 
.6511 
.6676 

g 
61 

.9848 
i.  
1.0151 

82 
S 

1.3121 
1-3252 
1-3383 

17 

.2956 

40 

..6840 

62 

1.0301 

85 

J-35I2 

18 

•3129 

4i 

.7004 

63 

1.0450 

86 

1.3640 

19 

•3301 

42 

.7167 

64 

1.0598 

87 

1-3767 

20 

•3473 

43 

•733° 

65 

1.0746 

88 

I-3893 

21 

•3645 

44 

•7492 

66 

1.0893 

99 

1.4018 

22 

.3816 

45 

•7654 

67 

1.1039 

90 

1.4142 

23 

•3987 

68 

1.1184 

Laying  Out  Figures  Having  Three,  Four,  Five,  Six  and 
Seven  Sides 

Here,  in  Fig.  54,  is  a  handy  method  of  laying  out  polygons 
or  figures  having  from  three  to  seven  equal  sides.  They 
are  only  half  finished,  but  this  shows  the  method  just  as  well 
and  can  be  completed  by  any  one  who  desires.  Starting 
with  a  side  AB,  which  is  the  same  in  them  all,  we  construct 
the  different  figures  as  follows: 

Three  Sides  or  Triangle 

Take  the  distance  AB  in  the  compass,  and  with  center  on 
A  draw  arc  BC,  then  with  center  on  B  draw  AC.  When 


HINTS    ON    LAYING    OUT 


73 


no.  54.  —  Laying  Out  Three  to  Seven-Sided  Figure. 


74 


MACHINE    SHOP    DRAWINGS 


they  cross  at  C  is  the  upper  point,  and  joining  these  three 
points  by  straight  lines  gives  the  triangle.  A  similar 
triangle  could  be  formed  by  connecting  A,  B  and  D. 

Four  Sides  or  Square 

Taking  C  as  a  center  and  distance  AB  in  the  compass, 
draw  a  complete  circle.  Draw  a  line  through  the  center 
from  D  to  T.  With  center  on  B,  draw  arc  ACV.  Then, 
with  center  on  E,  draw  arc  GH,  cutting  the  first  arc  at  /. 
This  gives  ABJ  as  one-half  the  square.  Drawing  arc  BCR, 
with  A  as  a  center,  gives  the  fourth  point  /  and  would  make 
the  square  AIJB. 

Five  Sides  or  Pentagon 

Take  the  distance  FG  or  FH  in  the  compass,  and  with 
the  center  on  A  mark  off  L  and  M.  Then  put  center  on  B 
and  mark  off  L  and  K.  This  gives  the  five  points  and  by 
joining  ABML  and  K  we  have  the  complete  pentagon. 

Six  Sides  or  Hexagon 

Having  the  circle  drawn  from  C  as  a  center,  the  radius 
CB  is  the  length  of  one  side  and  all  that  is  necessary  is 
to  step  off  the  six  points  ABQPO  and  N.  Connecting 
these  gives  a  complete  hexagon. 

Seven  Sides  or  Heptagon 

Take  the  distance  FP  in  the  compass,  and  with  center  on 
A  mark  off  F,  cutting  the  other  arc.  Then  moving  the 
center  to  B  mark  off  U,  to  V  and  mark  T,  and  so  on.  Com- 
ing back  the  other  way,  mark  off  R  from  B,  S  from  A ,  and 
check  T  by  marking  it  from  R.  Joining  ABVUTS  and  R 
gives  a  7-sided  figure  or  heptagon. 


HINTS    ON    LAYING    OUT 


75 


Another  Way  of  Laying  Out  Polygons 
Another  way  of  laying  out  equal-sided  figures  is  shown 
in  Fig.  55,  using  12  sides  or  a  duodecagon  as  an  example. 
Taking  one  side  as  AB,  from  A  draw  the  half -circle 
shown  with  a  radius  AB.  Divide  this  half-circle  into  12 
parts.  Draw  radial  lines  through  these  points,  as  A  i  C, 


A  B 

FIG.  55.  —  Another  Way. 

A  2  D,  etc.,  and  with  a  compass  step  off  the  distance  AB 
from  B  to  C,  from  C  to  D,  etc.  This  will  give  the  sides  of 
the  i2-sided  figure  as  shown  in  Fig.  55. 

Laying  Out  Bolt  Holes 

There  are  several  ways  of  laying  out  bolt  holes,  one  of 
which  is  shown  in  Fig.  56.     Draw  a  circle  the  size  of  the 


76  MACHINE    SHOP    DRAWINGS 

bolt  circle  and  draw  the  center  lines  crossing  at  right  angles. 
Divide  the  distance  OE  into  4  equal  parts  and  lay  off  EB 
equal  to  3  of  these  parts,  making  OB  equal  to  7  parts. 
Divide  the  diameter  CF  into  as  many  parts  as  there  are 


FIG.  56.  —  Handy  Way  to  Lay  Out  Bolt  Holes. 

bolt  holes  in  the  circle,  9  in  this  case.    Draw  a  line  from 
B  through  the  second  division  to  D.      Then  the  distance 
CD  is  the  distance  between  the  bolt  hole  centers.     Space 
around  to  see  that  no  mistake  has  been  made. 
This  may  be  no  easier  than  figuring  out  the  circum- 


HINTS    ON    LAYING    OUT 


77 


ference  of  the  bolt  circle  and  dividing  by  the  number  of 
bolts,  but  some  prefer  it  to  doing  calculations  of  any  kind. 

If  you  prefer  to  figure  it  out,  the  little  table  which  follows 
will  help.  This  gives  bolt  holes  from  3  to  12  in  number. 
Multiplying  the  number  given  after  the  right  number  of 
holes  by  the  diameter  of  the  bolt  circle  will  give  the 
center  distance  between  bolt  holes. 


No',  of 
Holes 

Distance  between  Bolt 
Centers  when  Diameter  of 
Bolt  Circle  is  i 

No.  of 
Holes 

Distance  between  Bolt 
Centers  when  Diameter  of 
Bolt  Circle  is  i 

3 

.866 

8 

.3827 

4 

.7071 

9 

•342 

I 

.5878 
.5 

10 

ii 

•3°9 
.2817 

7 

-4338 

13 

.2588 

Multipliers  for  Bolt  Hole  Centers 

If  the  bolt  circle  is  10  inches  in  diameter  and  there  are 
12  bolts,  the  distance  between  centers  will  be  10  X  .2588 
or  2.588  inches.  Or  if  the  bolt  circle  is  6  inches  and  has 
9  holes,  multiply  6  X  .342  and  get  2.052  inches  as  the  center 
distance  between  bolt  holes. 


A  Way  of  Finding  Pulley  Diameters 
Here  is  a  short  cut  pointed  out  by  Prof.  John  E.  Sweet 
that  may  come  in  handy  almost  any  time. 

In  changing  pulleys  on  line  shafts  or  other  places  it  may 
be  desirable  to  know  how  much  to  cut  out  of  or  add  to  a 
belt,  and  have  it  come  right.  That  is  to  say,  if  a  belt  runs 
over  two  pulleys  30  inches  in  diameter,  and  the  pulleys  were 


78  MACHINE    SHOP    DRAWINGS 

to  be  changed  to  36  inches,  the  belt  would  need  to  be  as 

much  longer  as  one  pulley  is  larger  around 'than  the  other. 

The  ordinary  way  to  determine  that  would  be  to  measure 

or  calculate  the  distance  around  each  pair  and  subtract  one 


B 


FIG.  57.  —  Finding  Pulley  Diameters. 

from  the  other;  but  that  is  not  at  all  necessary,  for  the 
difference  of  the  distances  around  two  pulleys  of  unequal 
size  is  the  same  as  the  distance  around  a  small  pulley 
whose  diameter  equals  the  difference  between  the  diameters 
of  the  two. 


HINTS    ON    LAYING    OUT 


79 


For  example:  we  have  a  belt  running  on  a  pair  of  i4-inch 
pulleys  and  wish  to  put  on  21 -inch  pulleys  instead,  how 
much  longer  must  the  belt  be? 

We  can  say,  offhand  and  without  any  figuring,  that  it 
must  be  the  same  as  the  distance  around  a  pulley  as  large 
as  the  difference  between  the  two  diameters  or  a  7-inch  pul- 
ley. Multiplying  7  inches  by  3^  gives  22  inches.  Finding 
the  circumference  of  the  14  and  21  inch  pulleys  in  the  same 
way,  we  have  44  and  66  inches  respectively  and  the  differ- 
ence is  22  inches,  the  same  as  the  diameter  of  the  7-inch 
pulley.  So  the  belt  must  be  22  inches  longer,  half  of  this 
being  taken  up  on  each  pulley. 

In  the  same  way  we  can  find  the  total  circumference 
of  any  number  of  pulleys  by  adding  the  diameters  and 
multiplying  the  sum  by  3}  or  3.1416  as  we  prefer.  This 
fact  is  probably  as  old  as  Egypt,  and  yet  it  may  be  new 
to  many,  that  the  circumference  A,  in  Fig.  57,  equals  the 
sum  of  the  circumference  of  the  other  two  pulleys,  B  and  C. 

Laying  Out  Equal  Spaces 

It  sometimes  happens  that  it  is  necessary  to  divide  an 
odd  dimension  into  equal  spaces.  In  the  case  shown  in 
Fig.  58  it  was  necessary  to  divide  i^  inches  into  n  equal 
parts.  So  instead  of  trying  to  figure  this  out  in  decimals 
the  scale  was  laid  on  at  such  an  angle  that  n  spaces  of 
some  divisions  of  the  scale  just  fitted  the  space;  in  this 
case  2flg-  is  taken  as  being  n  X  fV  =  f§-  In  the  same 
way  ii  X  1  =  2|  could  have  been  used,  but  it  is  better  to 
get  the  rule  as  nearly  right  angles  as  possible  across  the 
space. 

All  that  is  necessary  is  to  take  any  divisions  you  need, 


'8o  MACHINE   SHOP   DRAWINGS 

whether  64ths  or  inches,  and  work  at  each  division  selected. 
Then  drawing  lines  parallel  to  the  others  and  through 
these  points  gives  the  equal  divisions  desired. 


1 

> 

\l 


FIG.  58.  —  Laying  Out  Equal  Spaces. 

Screw  Threads 

In  the  old  days  the  draftsman  had  to  carefully  lay  out 
all  threads,  whether  they  were  2  or  20  to  the  inch,  and  draw 
them  to  the  right  angle  shown  at  A,  Fig.  59,  or  even  show 
the  tops  and  bottoms  of  the  threads  curved  as  was  shown 
in  the  paper  on  projection.  At  B  is  shown  a  square  thread 
drawn  in  a  similar  way,  while  C  illustrates  the  much  more 
sensible  way  of  showing  threads  that  is  now  almost  univer- 
sally used. 

Here  no  attempt  is  made  to  show  the  right  angle  or  the 
right  pitch,  but  only  to  indicate  that  a  thread  is  wanted,  to 
show  how  long  this  is  to  be  made,  what  kind  of  a  thread 


HINTS    ON   LAYING   OUT 


81 


TIG.  59.  —  Different  Ways  of  Showing  Screw  Threads. 


82  MACHINE    SHOP    DRAWINGS 

is  wanted  and  the  pitch.  When  we  consider  that  a  drawing 
is  no  longer  a  picture  to  please  the  eye  but  a  guide  for  the 
making  or  putting  together  of  some  useful  piece  of  machin- 
ery, the  good  sense  of  this  change  will  be  seen  at  once. 
This  not  only  saves  time  in  drawing  but  prevents  any 
attempt  to  measure  the  drawing  and  makes  it  necessary  to 
put  full  instructions  in  plain  language,  where  it  can  be 
seen. 

Some  make  a  practice  of  showing  a  thread  or  two  on  the 
end  of  the  piece  or  at  some  portion  of  its  length  to  indicate 
the  kind  of  a  thread,  but  this  seems  unnecessary  and  might 
be  misleading. 

Finding  the  Size  of  a  Broken  Ball 
This  shows  a  way  of  using  some  of  the  things  we  have 
learned  in  laying  out  work,  together  with  a  good  deal  of 
thought,  to  find  out  the  diameter  of  a  broken  ball  when 
only  a  part  of  the  ball  could  be  had  to  work  from.  This 
looks  like  a  sticker,  but  here  is  the  way  a  bright  apprentice 
boy  found  out  the  full  diameter  from  the  broken  piece. 

His  first  step  was  to  take  a  pair  of  dividers  as  at  B,  and 
find  the  largest  circle  he  could  draw  on  the  broken  part. 
Then  taking  his  drawing  board  he  laid  out  three  points 
abc  as  at  C,  by  using  the  dividers  to  measure  these  points 
on  the  circle  drawn  from  the  ball  itself.  The  next  step 
was  to  draw  a-circle  through  these  points  as  shown  at  C  by 
taking  a  distance  more  than  half-way  from  a  to  b  and 
striking  the  arcs  shown;  then  doing  the  same  between  a 
and  c  and  drawing  straight  lines  through  these  arcs  until 
they  cross  at  O  as  shown.  This  is  the  center  of  the  three 
points  ab  and  c. 


HINTS    ON    LAYING    OUT  83 

Then  the  line  db  at  D  drawn  to  the  diameter  of  the  circle 
laid  out  at  C  gave  the  part  represented  by  the  broken  piece. 
Taking  the  same  distance  as  was  used  in  the  dividers  to 
mark  the  circle  on  the  broken  ball,  and  setting  at  d  and  b, 


B  D 

FIG.  60.  —  Finding  the  Size  of  a  Broken  Ball. 

strike  the  arcs  eo  and  we  have  the  arc  deb  representing  the 
broken  piece  of  the  ball.  With  the  three  points  deb,  a  new 
circle  was  laid  out  through  these  three  points  which  gave  a 
circle  representing  the  full  size  of  the  ball. 


CHAPTER  V 

LAYING  OUT   SPUR  GEARS 

GEAR  wheels  and  gear  teeth  are  often  puzzling  to  those 
who  have  not  had  a  direct  acquaintance  with  them,  espe- 
cially the  questions  of  pitch  diameter,  diametral  and  cir- 
cular pitch.  As  with  most  problems  in  mechanics,  how- 
ever, there  is  nothing  difficult  about  it  if  we  go  slow  on 
learning  the  reasons. 

If  we  have  two  shafts  carrying  pulleys,  Fig.  61,  A  and  B, 
with  A  on  the  driving  shaft,  then  A  will  drive  B,  as  shown, 
as  long  as  the  load  on  B  is  not  too  great  to  be  driven  by 
friction.  The  distance  between  the  shafts  C  is  called  the 
center  distance  and  the  diameter  of  the  pulley  where  they 
drive  is  called  the  pitch  line,  so  the  "pitch  diameter,"  or 
driving  diameter,  is  the  diameter  at  this  line. 

But  friction  is  not  enough  to  drive  all  loads  and  it  is  not 
positive  enough  in  all  cases.  Some  machines  must  have  an 
exact  relation  between  the  speed  of  different  shafts  and  all 
slip  must  be  avoided.  So  we  build  up  projections  on  the 
face  of  A,  Fig.  62,  and  in  order  to  have  these  projections 
turn  we  cut  corresponding  grooves  in  B  for  these  to  fit  into. 
To  make  both  wheels  alike  and  to  have  the  teeth  uniform 
we  also  build  up  on  B  and  cut  grooves  in  A  so  we  have  gear 
teeth  in  both  wheels,  with  part  of  the  teeth  above  the  pitch 
and  part  below  it.  But  we  must  remember  this  pitch  line, 
as  it  is  the  most  important  part  of  the  whole  gear. 
84 


LAYING   OUT   SPUR   GEARS  85 

The  part  of  the  teeth  above  or  outside  the  pitch  line  is 
called  the  addendum  (added  to),  and  the  part  below  the  pitch 


FIG.  6 1  . —  Friction  Disk  to  Show  Pitch  Lines. 


FIG.  62.  —  Putting  Teeth  on  the  Disk. 

line  the  dedendum  (deducted  from).     In  the  language  of 
the  shop  the  addendum  becomes  the  point  and  the  dedendum 


86 


MACHINE    SHOP    DRAWINGS 


LAYING    OUT    SPUR    GEARS  87 

the  flank,  but  they  mean  just  the  same  thing.  To  keep  the 
points  of  the  teeth  from  rubbing  in  the  bottom  of  the  space 
an  additional  depth  is  cut  here  which  is  called  clearance. 
All  the  parts  of  the  tooth  are  shown  in  Fig.  63. 

Shapes  of  Teeth 

In  the  old  days  when  the  teeth  of  gears  were  mostly  cast 
it  was  necessary  for  the  patternmaker  or  millwright  to  know 
just  how  to  shape  the  teeth  to  have  them  run  smoothly. 
This  is  not  the  case  now,  as  the  teeth  are  cut  by  standard 
cutters,  which  are  supposed  to  have  the  right  form.  But 
it  is  well  to  have  some  idea  of  the  way  in  which  these  shapes 
are  laid  out  and  it  is  not  hard  to  understand. 

Formerly  it  was  all  the  style  to  use  the  epicycloidal  tooth. 
This  was  laid  out  by  rolling  a  small  circle  on  the  pitch  line 
and  letting  one  point  on  the  edge  of  the  small  circle  draw 
the  curve.  In  Fig.  64  the  laying  out  of  a  rack  tooth  is 
being  accomplished  by  the  pulley  resting  against  the  straight 
edge  at  the  bottom  which  represents  the  pitch  line  of  the 
rack.  Tie  a  pencil  to  the  pulley  rim  as  at  A  next  to  the 
line  and  roll  the  pulley  carefully  to  the  right.  The  pencil 
will  make  a  mark,  as  shown  by  the  curve  AB  when  it  has 
made  a  half  revolution..  The  size  of  the  pulley  or  rolling 
circle  varied  according  to  the  ideas  of  the  designer  and 
changed  the  shape  of  the  tooth.  For  gear  wheels  they 
rolled  the  circle  around  outside  the  pitch  circle  for  the  point 
of  the  tooth,  and  inside  the  pitch  line  for  the  flank  of  the 
tooth. 

The  Involute  Curve 

The  old  form  of  tooth  curve  has  given  way  almost  entirely 
to  what  is  called  the  involute  curve,  which  seems  to  give 


MACHINE    SHOP    DRAWINGS 


LAYING    OUT    SPUR    GEARS  89 

better  satisfaction  in  every  way,  although  some  still  use  the 
epicycloidal  form. 

The  involute  curve  can  be  produced  by  using  the  same 
pulley  as  before  and  wrapping  a  string  around  it  as  in 
Fig.  65.  A  pencil  tied  to  the  free  end  of  the  string  will 
make  the  curve  shown  if  it  is  kept  taut  and  swung  out  as 
shown.  In  the  case  of  a  gear  with  a  pitch  line  of  the  size 
shown,  this  would  give  the  correct  curve,  and  it  will  be  seen 
that  this  would  vary  in  direct  proportion  to  the  diameter 
of  the  pitch  line  of  the  gear  and  does  not  in  any  way  depend 
on  the  size  of  another  circle  as  in  the  other. 

With  a  rack  there  is  nothing  to  wrap  the  string  around, 
and  so  the  sides  of  the  teeth  are  a  straight  line,  as  will  be 
seen  in  all  the  cuts  showing  a  rack.  The  angle  generally 
used  is  143  degrees,  because  this  was  a  very  easy  angle  for 
the  patternmaker  to  lay  off  in  the  old  days,  being  the  same 
angle  as  the  worm  thread  and  the  Acme  thread. 

Drawing  the  Involute  Curve 

In  the  actual  laying  out  of  gear  teeth  we  do  not  use  a 
string,  but  draw  it  out  on  paper,  or  on  sheet  metal,  as  in 
Fig.  66.  Draw  the  circle,  which  is  the  pitch  diameter  of 
the  gear  wanted;  divide  part  of  the  circle  into  a  number 
of  equal  parts,  as  shown.  Line  i  i  is  at  right  angles  to 
a  line  drawn  from  i  to  the  center  of  the  circle,  2  2  is  a  right 
angle  to  a  line  drawn  from  2  to  the  center,  and  so  on.  Now 
take  the  distance  o  i  in  your  dividers  and  with  point  on  i 
draw  from  o  up  to  the  line  i  i.  Then  set  dividers  o  2  and 
with  point  on  2  draw  up  from  line  i  i  to  line  2  2,  and  so  on 
until  you  get  up  to  the  proper  hight  of  the  tooth.  The 
curve  is  shown  drawn  through  the  crosses  on  each  line.  It 


9o 


MACHINE    SHOP    DRAWINGS 


LAYING    OUT    SPUR    GEARS  91 

is  not  difficult  to  do  with  care,  but  is  not  often  needed  in  the 
shop,  though  it  is  a  good  thing  to  know  how. 

The  hight  of  the  tooth  above  or  outside  the  pitch  line  is 
what  determines  the  outside  diameter  of  the  gear  or  the  gear 
blank,  and  this  is  one  of  the  most  puzzling  parts  about  the 
gear  question.  The  pitch  diameter  is  not  marked  on  the 
gear,  and  if  we  attempt  to  measure  the  outside  of  the  gear 
we  go  astray  unless  we  thoroughly  understand  the  question. 
As  the  outside  diameter  is  dependent  on  the  pitch,  it  is 
necessary  for  us  to  understand  this  part  first. 

The  Pitch  of  Gears 

When  we  speak  of  a  screw  the  pitch  is  the  distance  from 
one  thread  to  the  other,  but  this  is  not  the  usual  way  to 
measure  gear  teeth,  although  it  is  done  in  some  cases.  The 
customary  way  is  to  give  the  number  of  teeth  for  every  inch 
in  pitch  diameter  as  the  pitch.  In  this  way  a  gear  4  inches 
in  diameter  on  the  pitch  line  with  48  teeth  would  be  called 
a  i2-pitch  gear,  because  there  were  12  teeth  for  each  inch 
of  pitch  diameter.  If  this  gear  had  40  teeth  it  would  be 
lo-pitch,  if  32  teeth,  8-pitch,  and  so  on. 

Pitch  is  sometimes  measured  from  tooth  to  tooth,  but 
should  be  designated  as  circular  pitch,  which  means  the 
distance  from  any  point  of  one  tooth  to  a  similar  point  of 
the  next  on  the  pitch  circle.  This  is  the  circumference  of  the 
pitch  circle  divided  by  the  number  of  teeth  on  the  gear. 
In  the  case  of  the  4-inch  pitch  diameter  gear  with  40  teeth 
the  circular  pitch  would  be  4  X  3.1416  divided  by  40,  or 
12.5664  divided  by  40,  which  gives  a  circular  pitch  of 
0.31416  inch,  or  a  little  more  than  three  to  the  inch.  Little 
confusion  is  likely  because  when  we  talk  of  circular  pitch 


92 


MACHINE    SHOP    DRAWINGS 


we  give  the  dimension  in  inches,  while  if  it  is  diametral  in 
pitch,  no  inches  are  mentioned,  simply  a  number,  as  2,  or  8, 
or  1 6  pitch,  as  the  case  may  be. 

The  comparative  table  shows  how  the  sizes  of  the 
different  pitches  compare  with  each  other  and  also  the  re- 
lation between  the  diametral-  and  circular-pitch  systems. 

Size  of  Gear  Blanks 

The  system  of  using  diametral  pitch  is  very  simple  in 
every  way,  especially  in  knowing  the  size  of  gear  blanks, 
but  it  has  the  drawback  of  not  meaning  anything  to  a  man 
unless  he  is  familiar  with  gears.  This  is  because  we  think 
of  dimensions  in  inches  or  other  definite  measurements. 
Ten  diametral  pitch  doesn't  mean  anything  to  us  until  we 
figure  it  out  in  inches,  which  is  easy  to  do.  If  there  are  10 
teeth  to  every  inch  in  diameter  and  there  are  3.1416  inches 
on  the  circumference  to  every  inch  of  diameter,  we  know 
that  there  are  10  teeth  for  every  3.1416  inches  of  the  cir- 
cumference. So  if  we  divide  3.1416  by  10,  or  whatever 
the  pitch  may  be,  we  get  the  circular  pitch  in  inches,  which 
tells  us  in  language  we  can  understand,  that  the  size  or 
spacing  of  the  teeth  is  0.314  inch,  or  a  little  over  3  to  the 
inch. 

In  Fig.  67  we  have  a  sketch  which  shows  how  the  pitch 
affects  the  size  of  the  teeth.  The  pitch  diameter  is  the  same 
in  all  these  cases,  but  we  see  the  difference,  which  is  very 
close  to  exact  size.  The  greatest  difficulty  is  in  getting  out 
of  the  notion  that  6  pitch,  for  example,  has  anything  to  do 
with  6  inches  or  $  of  an  inch.  When  you  want  to  think 
of  it  in  inches,  don't  forget  to  divide  3.1416  or  3!  by  the 
pitch  and  you  have  it. 


LAYING    OUT    SPUR    GEARS 


93 


The  great  advantage  of  the  diametral-pitch  system  is  in 
the  sizing  of  gear  blanks,  or  finding  the  outside  diameter 
of  the  gear.  The  teeth  are  designed  to  project  beyond 
the  pitch  line  just  one  part  of  the  pitch.  That  is,  a  ip-pitch 


FIG.  67.  —  Sizes  of  Teeth. 

gear  tooth  is  TV  of  an  inch  above  the  pitch  line,  and  as  there 
are  teeth  all  around  the  gear  we  must  add  2  parts  to  find 
the  total  diameter. 

A  60- tooth  gear  of  10  pitch  will  be  6  inches  pitch  diameter, 
and  the  outside  diameter  will  be  -^  more,  or  6fa,  or  6.2 


94 


MACHINE    SHOP    DRAWINGS 


inches  in  diameter.  A  6o-tooth  gear  of.  12  pitch  will  be 
5tV  outside  diameter,  and  if  it  was  4  pitch  it  would  be 
15!  inches  outside  diameter. 

All  this  can  be  made  into  rules,  which  are  put  in  as  easy 
a  form  as  possible  and  their  uses  explained. 

Working  these  out  by  a  gear  having  a  4-inch  pitch  diam- 
eter and  40  teeth,  we  find  the  diametral  pitch  by  dividing 
40  by  4  and  getting  10  as  the  answer. 

Outside  diameter  will  be  pitch  diameter,  4  inches,  plus 
2  parts  of  pitch  =  0.2  or  4.2  inches;  or,  having  only  dia- 
metral pitch  and  number  of  teeth,  we  have 

40  +   2   =   42, 

and  dividing  by  pitch,  or  10,  =  4.2  inches  as  before. 

With  outside  diameter  4.2  and  40  teeth  we  add  2  to  num- 
ber of  teeth,  making  42,  and  divide  by  outside  diameter,  or 

42  -r-  4.2  =  10  = 
diametral  pitch. 

To  find  pitch  diameter  we  can  divide  the  number  of 
teeth,  40,  by  the  diametral  pitch,  or  10,  giving  4  inches  as 
pitch  diameter.  Having  outside  diameter,  4.2,  and  num- 
ber of  teeth,  40,  we  add  2  to  the  number  of  teeth,  giving  42. 
Then  multiply  the  number  of  teeth,  40,  by  outside  diameter, 
40  X  4.2  =  1 68,  and  divide  by  42,  which  gives  4  inches  as 
pitch  diameter. 

These  rules  will  help  you  find  about  anything  you  want 
about  the  sizes  of  gears  or  gear  blanks. 

For  those  who  prefer  to  have  everything  figured  out  for 
them,  table  No.  3,  from  the  practice  of  the  A.  S.  Cook  Com- 
pany, Hartford,  Conn.,  will  be  found  very  useful  for  8,  10, 
12  and  16  pitch,  which  are  very  common.  For  other  cases 
the  rules  will  be  found  to  work  very  easily. 


LAYING    OUT    SPUR    GEARS 


95 


COMPARISON  OF  PITCHES 


TABLE  No.  i 

.  TABLE  No.  a 

Diametral 
Pitch 

Circular  Pitch 

Circular 
Pitch 

Diametral  Pitch 

ll 

2.5133* 

2* 

I-57I* 

4 

2.0944 

ij- 

1.676 

if 

1-7952 

if 

1-795 

if 

I-57I 
1.396 

1-257 

1 

1-933 
2.094 
2.185 

2f 

1.142 

if 

2.285 

3 

1.047 

IT^T 

2-394 

3i 

0.898 

ij 

2-513 

4 

0.785 

2.646 

5 

0.628 

2-793 

6 

0.524 

2.9=17 

7 

0.449 

i 

3.142 

8 

0-393 

H 

3-351 

9 

0-349 

j 

3-590 

10 

0.314 

if 

3.867 

IT 

0.286 

| 

4.189 

12 

0.262 

H 

4-570 

14 

0.224 

I 

5.027 

16 

0.196 

A 

5.585 

18 

20 

0-175- 
o.i57 

I 

6.283 
7.181 

22 

0.143 

8.378 

24 

0.131 

T\ 

10.053 

26 

O.I  21 

1 

12.566 

-     28 

O.I  1  2 

ft 

i6.755 

3° 

0.105 

1 

25-I33 

32 

0.098 

A 

50.266 

36 

0.087 

40 

0.079 

48 

0.065 

As  the  teeth  must  extend  below  the  pitch  line  as  far  as 
they  do  above  it,  to  allow  for  the  points  of  the  teeth  in  the 
other  gear,  the  length  of  the  tooth  will  be  two  parts  of  the 


96  MACHINE    SHOP    DRAWINGS 

TABLE  FOR  TURNING  AND  CUTTING  GEAR  BLANKS  FOR  STANDARD 
LENGTH  TOOTH  — FROM  ASA  COOK  Co. 


16     1 


Outside  Diameter 


i  i  .  ;! 
No.  of 
Teeth 


10  8 


135    |     -180    |     .216    |   .270 
Outside  Diameter 


4TV 


4A 

1 

•1  :  j 


sA 


5  T* 

STJ 

stl 

sH 

6 


1 

Is 
iS 

7& 
7f[i 

7A 


sA 


6A 
6A 

» 

fi5ff 

&A 

6A 
6A 


7A 


IS 


8A 

I 

8 

i 

8A 
8A 

S* 


LAYING    OUT    SPUR    GEARS 


97 


TABLE  FOR  TURNING  AND  CUTTING  GEAR  BLANKS  FOR  STANDARD 
LENGTH  TOOTH  —  FROM  ASA  COOK  Co.  —  Continued 


.135    I      -180     I     .216     I    .270 


Depth 

fTooth 


10  8 


Outside  Diameter 


|. 

6A 

6* 

£ 

!t 
a* 


f':f 


7A 

I 


8 

8A 

8A 


9 


9A 
10 

ioA 


"A 


io  A 


nf 
n| 

12 
«t 

I2| 
12* 


I 

13! 


14 

i4l 


Hi 
14* 


a 


No.  of 
Teeth 


133 

134 
i,35 
136 

i37 
138 
139 

140 
141 

142 

143 

144 

145 

146 

147 
148 

149 
150 

152 
1 53 
154 

3 

i57 
tS8 


Outside  Diameter 

lift 

"A 

13  A 

X3i 
14 


12 

"A 
«A 


15 


i3A 


14 


X4A 

I41? 

?4$ 
*4A 


17  A 


98  MACHINE    SHOP    DRAWINGS 

pitch  plus  the  allowance  for  clearance  at  the  bottom  of 
the  space.  • 

The  clearance  allowed  by  Brown  &  Sharpe  is  obtained 
by  adding  one-eighth  of  the  tooth  depth.  A  lo-pitch  tooth 
will  be  f^,  or  0.20,  and  one-eighth  of  this  is  0.016,  so  that 
the  total  tooth  depth  for  a  lo-pitch  gear  is  0.216  inch. 

The  thickness  of  the  tooth  at  the  pitch  line  will,  of  course, 
be  one-half  the  circular  pitch,  as  the  circular  pitch  includes 
a  tooth  and  a  space.  We  found  the  circular  pitch  of  a 
lo-diametral-pitch  tooth  to  be  one-tenth  of  3.1416,  or  0.314, 
and  half  of  this  is  0.157;  we  can  find  this  direct  by  dividing 
0.157,  which  is  one-half  of  0.314,  by  the  pitch. 

French  or  Metric  Gears 

The  French  speak  of  "their  gears  in  a  different  way,  and 
as  there  are  a  number  of  French  automobiles  in  this  coun- 
try, it  may  come  handy  to  know  just  what  gears  you  need 
to  replace  one  of  these.  Instead  of  diametral  pitch  they 
speak  of  "module,"  which  is  the  pitch  diameters  in  milli- 
meters divided  by  the  number  of  teeth  in  a  gear;  so  if  the 
pitch  diameter  is  100  millimeters  and  there  are  40  teeth  the 
module  is  2.5,  which  is  very  nearly  the  same  as  a  jo-diametral 
pitch. 

Having  the  number  of  teeth  and  the  module,  we  find  the 
outside  diameter  by  adding  2  to  the  number  of  teeth  and 
multiplying  by  the  module.  Taking  the  same  example 
we  have 

40  +   2  =   42, 

and 

42  X  2.5  =  105 

millimeters  as  the  outside  diameter. 


LAYING    OUT    SPUR    GEARS 


99 


A  FEW  GEARING  RULES 


Having 

To  Find 

Rule 

i  Pitch  diameter  and 
number  of  teeth 

Diametral  pitch 

Divide  number  of  teeth 
by  pitch  diameter 

2  Outside  diameter  and 
number  of  teeth 

Diametral  pitch 

Add  2  to  number  of  teeth 
and  divide  by  outside 
diameter 

3  Number  of  teeth  and 
diametral  pitch 

Outside  diameter 

Add  2  to  number  of  teeth 
and  divide  by  diam- 
etral pitch 

4  Pitch  diameter  and 
diametral  pitch 

Outside  diameter 

Add  to  pitch  diameter  2 
parts  of  diametral 
pitch 

5  Number  of  teeth  and 
diametral  pitch 

Pitch  diameter 

Divide  number  of  teeth 
by  the  diametral  pitch 

6  Number  of  teeth  and 
outside  diameter 

Pitch  diameter 

Add  2  to  number  of  teeth 
and  divide  this  into 
the  product  of  the  num- 
ber of  teeth  and  the 
outside  diameter 

Laying  Out  the  Teeth 

While  not  many  outside  of  the  drawing  room  have  to 
do  the  laying  out  of  gear  teeth,  it  may  not  come  amiss  to 
know  how  it  is  done.  Fig.  68  shows  the  single-curve  tooth 
method.  The  first  thing  is  to  draw  the  pitch  circle.  Then 
draw  the  smaller  half-circle  with  the  compasses  set  to  one- 
half  the  pitch  radius  as  at  A.  Take  one-half  this,  or  one- 
quarter  the  pitch  radius,  and  with  the  center  on  B  draw 
the  arc  C.  Where  this  cuts  the  half-circle  is  the  base  for 
the  base  circle  for  tooth  arcs,  as  shown.  This  should  then 


MACHINE    SHOP    DRAWINGS 


1 


.    •.  3 

I        S       ! 


HI!.' 

5     M  "     K   1 


LAYING    OUT    SPUR    GEARS 


101 


be  drawn  all  around  inside  the  pitch  circle,  and  used  as  a 
base  from  which  to  draw  the  tooth  arcs  after  the  teeth  have 
been  spaced  properly. 

Pressure  Angles 

This  term  is  applied  to  indicate  the  angle  at  which  one 
tooth  presses  against  the  other  and  affects  the  laying  out 
of  the  teeth.  This  can  best  be  shown  by  showing  a  gear 


FIG.  69.  —  Standard  I4i-Degree  Tooth. 

in  a  rack,  as  in  Fig.  69.  This  shows  a  i4^-degree  tooth, 
which  means  that  the  rack  tooth  has  sides  at  14^  degrees 
from  the  perpendicular,  or  29  degrees  total  angle,  as 
shown.  The  pitch  circle  of  the  gear  is  drawn  in  contact 
with  the  pitch  line  of  the  rack.  Then  draw  the  line  AB, 
and  after  this  the  pressure  line  CD  at  14 \  degrees.  Next 
draw  a  line  from  the  center  to  the  pressure  line  and  at  right 
angles  to  it,  and  where  they  meet  is  the  right  place  for  the 


102 


MACHINE    SHOP    DRAWINGS 


base  circle  of  the  tooth  arcs,  as  shown.  Fig.  70  shows  the 
same  thing  for  the  ao-degree  pressure  angle  and  the  stub 
tooth. 

The  Stub  Tooth 

There  is,  of  course,  a  difference  of  opinion  both  as  to 
the  pressure  angle  and  the  length  of  tooth.  Many  are  now 
advocating  the  2o-degree  angle  in  connection  with  a  shorter 


FIG.  70.  —  Stubbed  2o-Degree  Tooth. 

tooth,  among  the  earliest  and  most  persistent  being  the 
Fellows  Gear  Shaper  Company,  who  began  working  along 
this  line  in  1899.  This  gives  a  broader  base  to  the  tooth 
and  makes  a  stronger  gear,  especially  on  small  pinions 
where  it  is  most  needed. 

In  the  Fellows  system  there  is  no  fixed  relation  between 
the  length  of  the  stub  tooth  and  the  standard  tooth.  In- 
stead the  length  varies,  as  shown  by  the  following  table, 
which  also  gives  proportions  of  parts  of  the  tooth: 


LAYING    OUT    SPUR    GEARS 


103 


TOOTH  DIMENSIONS  OF  FELLOWS  STUB-TOOTH  GEAR 


Mark  on 

Stub  Tooth 

Has  Depth 
of 

Thickness 

Above  Pitch 

Below  Pitch 

Cutter 

Pitch 

Standard 
Tooth 

PitchDLine 

Line 

Line 

4 

4 

5 

0-3925 

0.200 

0.250 

^ 

5 

0.314 

0.1429 

0.1785 

f 

6 

8 

0.2617 

0.125 

0.1562 

3j 

7 

9  ' 

0.2243 

O.I  1  1 

0.1389 

A 

8 

10 

0.1962 

O.IOO 

0.125 

•j8j- 

9 

ii 

0.1744 

0.0909 

0.1137 

T$. 

10 

12 

0.157 

0.0833 

0.1042 

H 

12 

14 

0.1308 

0.0714 

0.0893 

This  shows  that  with  the  Fellows  system  a  stub  tooth 
of  4-pitch  will  be  only  as  deep  as  a  standard  tooth  of  5-pitch, 
or  a  Q-stub  will  be  the  same  depth  as  an  1 1  standard  pitch. 

The  Nuttall  Company  have  also  been  advocates  of  the 
short  tooth,  but  they  have  adopted  a  fixed  depth  based 
on  the  circular  pitch  of  the  gear.  In  the  standard  tooth 
the  addendum  is  0.3183  times  the  circular  pitch,  while 
Nuttall  advises  only  0.25.  The  dedendum  is  0.30  instead 
of  0.3683,  and  as  the  clearance  is  the  same,  the  total  depth 
is  0.55  times  the  circular  pitch  instead  of  0.6866,  so  that  we 
can  say  the  Nuttall  stub  tooth  is  only  0.8  as  long  as  the 
standard  tooth  in  all  cases. 

Having  turned  the  gear  blank  according  to  the  table, 
or  by  calculation,  it  only  remains  to  set  the  cutter  and  gage 
the  depth  of  cut.  For  this  purpose  the  gear-tooth  gages 
are  made,  and  Fig.  71  shows  how  it  is  used.  A  gage  is 
made  for  every  pitch,  and  usually  kept  in  the  tool  room 
unless  a  man  has  a  set  of  his  own. 


104 


MACHINE    SHOP    DRAWINGS 


Generating  Gear  Teeth 

We  have  not  gone  into  the  theory  of  gear-tooth  shapes, 
as  this  is  not  necessary  in  the  making  of  gears,  but  is  a 


FIG.  71.  —  Using  Gear  Tooth  Depth  Gage. 


FIG.  72.  —  Generating  the  Gear  on  the  Fellows  Gear  Shaper. 

question  to  be  decided  by  the  designer  in  the  drawing  room 
and  tool  room.  The  generating  of  teeth,  however,  as  done 
on  the  Fellows  gear  shaper,  is  interesting  in  several  ways. 


LAYING    OUT    SPUR    GEARS  105 

The  cutter  is  really  a  steel  gear  with  hardened  teeth,  as  at 
A,  Fig.  72.  This  moves  up  and  down  across  the  face  of  the 
gear  and  planes  the  teeth.  In  starting  to  cut  a  gear,  the 
cutter  is  fed  straight  into  the  gear  blank  to  the  proper 
depth,  then  both  the  cutter  and  the -blank  are  revolved  to- 
gether so  that  the  teeth  are  cut,  one  after  the  other,  as  the 
cutter  and  gear  blank  roll  together.  It  is  a  very  ingenious 
process,  and  one  cutter  cuts  all  gears  of  that  pitch  regard- 
less of  size. 

Rotary  Cutters 

In  usual  practice  a  set  of  eight  rotary  cutters  is  used  for 
cutting  all  gears,  and  these  are  standardized  to  such  an 
extent  that  all  agree  on  the  cutters  to  be  used  for  different 
sized  gears,  a  set  of  eight  being  required  for  each  pitch. 
These  are  divided  as  follows: 

No.  i  cutter  will  cut  gears  from  135  to  a  rack. 
No.  2  cutter  will  cut  gears  from  55  to  134. 
No.  3  cutter  will  cut  gears  from  35  to  54. 
No.  4  cutter  will  cut  gears  from  26  to  34. 
No.  5  cutter  will  cut  gears  from  21  to  25. 
No.  6  cutter  will  cut  gears  from  17  to  20. 
No.  7  cutter  will- cut  gears  from  14  to  16. 
No.  8  cutter  will  cut  gears  from  12  to  13. 

When  using  these  cutters  the  proper  depth  and  thickness 
at  pitch  line  are  shown  by  the  following  table: 


io6 


MACHINE    SHOP    DRAWINGS 


PROPORTIONS  OF  GEAR  TEETH 


2$ 
0 

Depth  to  be 
Cut  in 
Gear 

Thickness 
of  Tooth 

PitchLine 

1$ 
$ 

Depth  to  be 
Cut  in 
Gear 

Thickness 
of  Tooth 

PitchatLine 

Jj 

1.7*6* 
1.438 

i.*57' 

1.047 

II 

12 

0.196* 
0.180 

0.143* 
0.131 

if 

1-233 

0.898 

14 

0.154 

O.I  I  2 

2 

1.078 

0.785 

16 

0.135 

0:098 

3j 

0.958 

0.697 

18 

O.  I  20 

0.087 

2* 

0.863 

0.628 

20 

0.108 

0.079 

2l 

0.784 

0.570 

22 

0.098 

0.071 

3 

0.719 

0.523 

24 

0.090 

0.065 

3i 

0.616 

0.448 

26 

0.083 

0.060 

4 

0.539 

0-393 

28 

0.077 

0.056 

I 

0.431 
0-359 

0.3H 
0.262 

30 
32 

0.072 
0.067 

0.052 
0.049 

7 

0.308 

0.224 

36 

0.000 

0.044 

8 

0.270 

0.196 

40 

0.054 

0.039 

9 

0.240 

0.175 

48 

0.054 

0.033 

10 

0.216 

0.157 

CHAPTER  VI 

LAYING  OUT  BEVEL  GEARS 

BEVEL  gears  are  entirely  different  in  many  respects  from 
spur  gears,  and  instead  of  being  able  to  easily  figure  out 
the  outside  diameter  of  the  blanks,  as  in  the  case  of  spur 
gears,  it  is  necessary  to  lay  them  out  in  each  case  unless  you 
happen  to  have  them  worked  out  for  exactly  the  conditions 
you  have  in  hand.  , 

Bevel  gears  which  transmit  power  at  right  angles  and 
which  have  the  same  number  of  teeth  are  often  called 
miter  gears,  but  they  are  simply  bevel  gears  in  which  both 
gears  are  exactly  alike  and  in  which  the  pitch  line  is  45 
degrees  from  the  center  line  of  the  gear. 

Of  course  it  is  better  to  become  entirely  familiar  with  the 
terms  used  in  connection  with  bevel  gears  so  that  there  may 
be  no  confusion  and  that  we  can  readily  understand  what 
is  being  talked  about.  For  this  purpose  we  reproduce 
Fig.  73  having  the  various  portions  named,  and  an  occa- 
sional reference  to  this  will  avoid  any  mistakes  being  made. 

Assume  that  we  have  a  pair  of  bevel  gears  to  lay  out, 
one  having  24  and  the  other  32  teeth  of  8  pitch.  We 
begin  exactly  as  in  the  case  of  spur  gears,  finding  our  pitch 
diameters  in  the  same  way.  Dividing  24  and  32  teeth  by  the 
pitch,  we  find  that  the  pitch  diameters  are  3  and  4  inches, 
respectively. 

As  these  are  to  be  at  right  angles,  draw  center  lines  A  A 
107 


io8 


MACHINE    SHOP    DRAWINGS 


and  BB  at  right  angles  to  each  other,  crossing  at  O,  as  shown 
in  Fig.  74,  which  becomes  the  center  of  our  operations. 
Measure  ij  inches  each  side  of  A  A  and  2  inches  each  side 
of  BB,  and  draw  in  the  pitch  diameter  lines  PP1P2  as  a 
starting-point. 

These  lines  show  the  pitch  diameter  of  both  gears,  and 
the  next  step  is  to  draw  a  line  through  O  connecting  P  and 


FIG.  73.  —  The  Names  of  Parts  and  Angles  of  a  Bevel  Gear. 

P2,  and  another  line  from  O  to  P1.  These  are  the  pitch 
lines  on  which  the  teeth  roll  together  the  same  as  in  a  spur 
gear. 

The  length  of  the  teeth  is  found  in  exactly  the  same  way 
as  for  spur  gears,  but  before  doing  this,  draw  the  line  EE 
at  right  angles  to  the  pitch  center  line,  as  shown,  these  lines 
giving  what  is  known  as  the  edge  angle,  as  shown  in  Fig.  73. 
As  these  gears  are  8-pitch,  take  one  pitch  or  J  of  an  inch 


LAYING  OUT  BEVEL  GEARS 


,109 


and  lay  it  off  on  the  line  EE,  each  side  of  the  pitch  center 
line,  as  F  and  G.  The  line  OF  then  gives  the  outside  angle 
of  the  gear,  and  after  laying  off  clearance,  as  GH,  we  have  the 
line  OH  as  the  cutting  angle,  or  the  line  on  which  the  mill- 


FIG.  74.  —  Finding  the  Angles  of  a  Bevel  Gear. 

ing  cutters  must  travel  to  cut  the  tooth  to  the  right  depth 
along  its  whole  length. 

This  shows  very  clearly  how  the  depth  of  a  tooth  in  a 
bevel  gear  varies  all  along  its  length,  growing  smaller  as  it 
approaches  the  center.  To  show  this,  we  have  drawn  the 


no  MACHINE    SHOP    DRAWINGS 

teeth  in  section  X  and  Y  to  give  an  idea  of  the  difference 
in  the  size  of  the  tooth  at  these  two  points  and  also  to  show 
how  the  clearance  acts  the  same  as  in  a  spur  gear. 


TIG.  75.  —  Finding  the  Bevel  Gear  Cutter. 

Selecting  the  Culler 

If  the  gears  have  been  laid  out  carefully,  you  will  have  all 
the  necessary  dimensions  and  angle  for  turning  the  blank 
and  cutting  teeth,  but  it  will  be  necessary  to  do  a  little 


LAYING    OUT    BEVEL    GEARS  ill 

more  laying  out  before  you  can  decide  on  what  cutter  is 
to  be  used,  as  this  is  different  from  spur  gear  cutting  in  this 
respect.  This  brings  us  to  Fig.  75,  which  is  the  same  pair 
of  gears  laid  out  to  the  angles  found  before,  and  the  lines" 
OA  and  OB  are  right  angles  to  each  other  and  representing 
the  centers  of  two  shafts  on  which  the  gears  run.  Through 
the  edge  angle  draw  the  line  meeting  A  and  B,  as  shown, 
and  measure  the  distance  between  the  point  where  the  pitch 
line  cuts  this  and  A,  also  from  C  to  B.  These  distances 
will  be  1 1  and  3T5ff  inches,  respectively. 

In  selecting  the  cutter,  we  assume  that  we  are  dealing 
with  a  spur  gear  having  the  same  tooth  as  the  outside  end 
of  the  bevel  gear  tooth,  and  a  diameter  that  corresponds 
to  this  as  found  by  these  lines  at  right  angles  of  the  pitch 
line  OC. 

The  distances  we  have  measured  thus  become  one-half 
the  diameter  of  spur  gears  having  the  teeth,  and  we  multiply 
these  distances  by  2,  securing  a  pitch  diameter  of  3!  inches 
for  the  small  gear  and  6|  inches  for  the  large  gear.  Mul- 
tiply these  diameters  by  the  pitch  to  find  how  many  teeth 
of  this  pitch  would  be  in  a  spur  gear  of  the  same  size,  and 
we  have  30  teeth  for  the  small  gear  and  53  teeth  for  the  large 
gear. 

Looking  up  the  table  of  gear  cutters,  we  find  that  a  spur 
gear  of  30  teeth  requires  a  No.  4  cutter  and  one  of  53  teeth 
a  No.  3  cutter,  so  that  we  select  these  as  proper  cutters  to 
be  used  in  these  gears. 

If  we  had  been  dealing  with  spur  gears  of  3  and  4  inches 
in  diameter  and  the  number  of  teeth  which  the  gears  actu- 
ally have,  we  would  have  used  a  No.  5  cutter  for  the  small 
gear  and  a  No.  4  cutter  for  the  larger  gear,  but  for  the  bevel 


112  MACHINE    SHOP    DRAWINGS 

gears  it  has  been  found  necessary  to  select  the  proper 
cutter  in  this  way  in  order  to  secure  smooth  running  gears. 
A  very  little  practice  in  the  laying  out  of  bevel  gears  of 
various  sizes  and  having  shafts  at  different  angles  will 
enable  any  one  to  become  familiar  with  this  work  and  to 
lay  them  out  without  making  mistakes  of  any  kind.  It  is 
well  to  become  thoroughly  familiar  with  the  names  of  the 
various  parts  and  angles  so  as  to  avoid  any  chance  of  con- 
fusion. 


CHAPTER  VII 

THE  WORM  AND  WORM  WHEEL 

THE  worm  and  worm  wheel  may  be  called  a  combina- 
tion of  a  screw  and  a  gear,  the  screw  driving  the  gear  by 
forcing  its  teeth  along  in  the  thread  as  the  screw  turns. 
With  very  few  exceptions  the  screw  turns  the  worm  and 
cannot  be  reversed,  although,  with  a  sharp  enough  angle 
to  the  thread,  the  wheel  can  be  made  to  turn  the  worm. 
When  this  is  done,  the  worm  wheel  has  a  straight  face 
and  the  combination  comes  under  the  head  of  spiral  gears, 
though  the  principle  is  the  same. 

There  are  serious  differences  of  opinion  about  worm 
wheels,  many  of  our  best  designers  contending  that  a 
worm  wheel  with  a  straight  face  is  as  good  as  one  with  a 
face  that  is  hobbed  to  fit  the  worm,  but  as  we  are  more 
accustomed  to  the  curved  or  hollow  faced  worm,  we  will 
consider  that  first. 

The  first  thing  to  do- is  to  learn  the  names  of  the  different 
parts  as  shown  in  Fig.  76  so  that  all  terms  used  will  be  clearly 
understood. 

The  next  thing  is  to  decide  on  the  ratio  between  the  worm 
and  the  wheel.  Suppose  we  wish  to  reduce  the  speed  of 
a  motor  from  2,000  to  50.  We  divide  2,000  by  50  and  find 
that  it  is  a  reduction  of  40  to  i ;  that  is,  the  screw  or  worm  must 
turn  40  times  to  one  turn  of  the  worm  wheel,  and  for  a  single- 
113 


114 


MACHINE    SHOP    DRAWINGS 


thread  worm  the  wheel  must  have  40  teeth  as  the  wheeel 
will  be  moved  one  tooth  for  every  turn  of  the  worm. 

Calling  the  worm  i  inch  in  diameter  and  a  lead  of  {  inch 
or  4  threads  to  the  inch,  the  wheel  must  have  40  teeth, 
^  inch  apart  on  the  pitch  line,  or  J  inch  circular  or  linear 
pitch. 

This  means  that  the  pitch  circumference  will  be  40  X  J 
inch  or  10  inches,  and  this  divided  by  3.1416  will  give  the 
pitch  diameter  of  the  worm  gear.  This  is  3.182  inches  as 
the  pitch  diameter  of  the  worm.  The  diametrical  pitch 


TIG.  76.  ••—  Terms  Used  in  Worm  Gearing. 

is  found  by  multiplying  3.1416  by  the  threads  per  inch  of 
the  worm  as  measured  along  it,  without  regard  to  whether 
it  is  single,  double,  triple,  or  how  many  threads  are  cut  on 
it.  In  this  case  we  have  4  threads  to  the  inch  so  that  the 
diametrical  pitch  will  be  3.1416  X  4  =  12.5664. 

Looking  up  a  table  of  tooth  parts  for  gears  with  cir- 
cular and  diametrical  pitch  we  find  that  the  addition  or 
distance  above  the  pitch  line  is  .0796,  the  depth  of  space 
below  the  pitch  line,  including  clearance,  .0921,  making  a 
total  of  .1717  inches. 

So  we  lay  off  .0796  each  side  of  the  pitch  diameter  of 
3.182,  making  the  thread  diameter  3.3412  inches  in  diameter. 


THE    WORM    AND    WORM    WHEEL  115 

To  find  the  total  or  outside  diameter  of  the  blank  we  must 
measure  the  corners  from  the  drawing,  as  they  depend  on 
the  width  of  face  we  allow,  and  this  varies  according  to  the 
ideas  of  the  designer. 


Acmezq-Degrce  Screw  Thread 


American  Machlnkt.  If. g 

FIG.  77.  —  Acme  and  Brown    &  Sharpe  ag-Degree  Worm  Thread 

The  thread  of  the  worm  is  deeper  than  the  thread  of  an 
ordinary  screw  and  has  an  angle  of  29  degrees  as  seen  in 
Fig.  77,  while  the  depth  and  the  flats  are  given  in  the  table. 

There  seems  to  be  some  confusion  among  mechanics 


n6 


MACHINE   SHOP    DRAWINGS 


regarding  the  29-degree  Acme  standard  screw  thread  and 
the  Brown  &  Sharpe  zg-degree  worm  thread. 

Circ;e 


FIG.  78.  —  Showing  Undercut  Teeth. 

In  Fig.  77  the  difference  between  the  threads  of  the  same 
pitch  in  the  two  systems  is  plainly  shown.  These  are  of 
threads  of  one-inch  linear  pitch  drawn  to  scale  to  the 


THE   WORM   AND   WORM    WHEEL 


117 


proportions  given  by  the  thread  formulas  in  connection 
with  the  complete  tables  of  the  two  systems  of  threads  as 
given  on  pages  following. 

•pitch  Circle 


Jlmtrican  Machinist.  N.  r. 


FIG.  79.  —  Excessive  Undercutting. 

The  angle  of  the  teeth  depends  on  the  pitch  of  the  worm 
and  its  diameter,  this  being  determined  by  laying  out 
the  worm  on  paper  and  drawing  one  thread. 


u8 


MACHINE    SHOP    DRAWINGS 


GEAR  WHEELS 


TABLE  OF  TOOTH  PARTS  —  CIRCULAR  PITCH  IN  FIRST  COLUMN 


•S 

il 

I" 

"3-9 

(A 

1 
S 

M 
o. 

J| 

j 

11 

i 

c 

•1 

Js 

•OJJ 

C  3 

ffl 

•sg 

^* 

°J3 

^ 

— 

ctf  u 

fi 

u  2  c 

W"^ 

^jH 

•£  ° 

•si 

J3*3 

xH 

5 

|K 

I 

H 

i2 

I"8 

I2 

i 

IH 

I' 

r 

? 

P 

/ 

S 

jy 

N-, 

ir+f 

PX.3I 

rx*» 

2 
I  J 

A 

1.5708 
I-6755 

I.OOOO 

•9375 

.6366 
.5968 

1.2732 
1-1937 

.7366 
.6906 

1-3732 
1.2874 

.6200 
•5813 

.6700 
.6281 

i} 

if 

i 

1-7952 
1-9333 

.8750 
.8125 

•5570 
•5173 

1.1141 
1.0345 

•6445 
•5985 

i.  2016 
1.1158 

•5425 
•5038 

.5863 
•  5444 

l| 

i 

2.0944 

.7500 

•4775 

•9549 

•5525 

1.0299 

•4650 

•5025 

xrV 

2-1855 

•7187 

•4576 

•5294 

.9870 

•4456 

.4816 

i| 

-A- 

2.2848 

•6875 

•4377 

^8754 

•5064 

•9441 

.4262 

.4606 

ii 

i 

2.3562 

.6666 

.4244 

.8488 

.4910 

•4133 

.4466 

If« 

If 

2.3936 

•6562 

.4178 

.8356 

.4834 

.9012 

.4069 

•4397 

f 

2.5133 

.6250 

•3979 

•7958 

.4604 

•8583 

•3875 

.4188 

1  A 

H 

2.6456 

•5937 

.3780 

.7560 

•4374 

.8156 

.3681 

.3978 

i 

2.7925 

•5625 

.358i 

.7162 

•4143 

•7724 

.3488 

.3769 

JA 

2.9568 

•53" 

•3382 

.6764 

•3913 

•7?95 

•3294 

•3559 

i 

3.1416 

.5000 

•3183 

.6366 

•3683 

.6866 

.3100 

•3350 

'I 

1 

3-35io 
3-5904 
3.8666 
3.9270 
4.1888 

.4687 

.4062 
.4000 
•3750 

•  2984 

.2546 
•2387 

•  5968 
•5570 
•5173 
.5092 

•4775 

•3453 
•3223 
•2993 
.2946 
.2762 

•6437 
.6007 
•5579 
•5492 
•5150 

.2906 
•  2713 
•  2519 
.2480 
•2325 

-3141 
•2931 
.2722 
.2680 
-2513 

fi 

xA 

4-5696 

•3437 

.2189 

•4377 

•2532 

•4720 

.2131 

•  2303 

i 

4.7124 

•3333 

.2122 

•4244 

•2455 

•4577 

.2066 

-2233 

1 

i'  • 

5-0265 

•3125 

.1989 

•3979 

•  2301 

.4291 

.1938 

.2094 

1 

i 

5-2360 

.3000 

.1910 

.3820 

.2210 

.4120 

.1860 

.2010 

1 

ij 

5.4978 

•2857 

.l8l9 

•3638 

.2105 

•3923 

.1771 

.I9M 

A 

x| 

5-5851 

.2812 

.1790 

•358i 

.2071 

.3862 

•  1744 

.1884 

THE    WORM    AND    WORM    WHEEL  119 

GEAR  WHEELS  —  Continued. 
TABLE  or  TOOTH  PARTS  — CIRCULAR  PITCH  IN  FIRST  COLUMN 


|| 

- 

*! 

1 

^ 

81' 

•8 

\ 

1 

•g 

"oja 

S 

Su  § 

B 

V 

"•§ 

!• 

ll 

1 

a 

"8 

• 

Ili 

|| 

ll 

I! 

^•3 

Jr 

J>§ 

1> 

B 

] 

sla 

?S 

"o"o 

E.1J 

"|j3 

Sr* 

5d 

D 

s 

H 

< 

* 

Q 

^ 

5 

5 

P' 

? 

p 

t 

5 

IT 

H-/ 

D"+f 

P'X,I 

P'X-.sss 

i 

2 

6.2832 

.2500 

.1592 

.3183 

.1842 

•3433 

•155° 

•1675 

4 

2\ 

7.0685 

.2222 

.1415 

•2830 

•1637 

•3052 

-1378 

.1489 

3*5 

2\ 

7.1808 

.2187 

•1393 

-2785 

.1611 

•3003 

•1356 

.1466 

f 

3* 

7-3304 

•  2143 

.1364 

.2728 

•1578 

.2942 

.1328 

.1436 

| 

2* 

7.8540 

.2000 

•1273 

.2546 

•1473 

.2746 

.1240 

•1340 

| 

2| 

8-3776 

.1875 

.1194 

•2387 

.1381 

•2575 

.1163 

.1256 

T4j- 

2f 

8.6394 

.l8l8 

.1158 

•2316 

.1340 

.2498 

.1127 

.1218 

£ 

3 

9.4248 

.1666 

.Io6l 

.2122 

.1228 

.2289 

•  1033 

.1117 

!• 

10.0531 

.1562 

•0995 

.1989 

.1151 

.2146 

.0969 

.1047 

3* 

10.4719 

.1500 

•0955 

.1910 

.1105 

.2060 

•0930 

.1005 

10.9956 

.1429 

.0909 

.1819 

.1052 

.1962 

.0886 

•0957 

4 

12.5664 

.1250 

.0796 

•1591 

.0921 

.1716 

•0775 

.0838 

4i 

14.1372 

.1111 

.0707 

.1415 

.0818 

.1526 

.0689 

•0744 

5 

15.7080 

.1000 

.0637 

•1273 

•°737 

•1373 

.0620 

.0670 

A 

Si 

16.7552 

•0937 

•0597 

.1194 

.0690 

.1287 

.0581 

.0628 

A 

5* 

17.2788 

.0909 

•0579 

.1158 

.0670 

.1249 

.0564 

.0609 

t 

6 

18.8496 
20.4203 

•0833 
.0769 

•0531 
.0489 

.I06l 
.0978 

.0614 
.0566 

.1144 
•i°55 

•0517 
.0477 

-0558 
•0515 

7 

21.9911 

.0714 

•0455 

.0910 

.0526 

.0981 

-0443 

.0479 

T\ 

71 

23.5619 

.0666 

.0425 

.0850 

.0492 

.0917 

.0414 

.0446 

1 

8 

25-1327 

.0625 

.0398 

.0796 

.0460 

.0858 

.0388 

.0419 

^ 

9 

28.2743 

•0555 

•0354 

.0707 

.0409 

.0763 

•0344 

.0372 

^5 

10 

31-4159 

.0500 

.0318 

.0637 

.0368 

.0687 

.0310 

•0335 

iV 

2fr 

16 

20 

50.2655 
62.8318 

.0312 
.0250 

.0199 
•0159 

.0398 

.0230 
.0184 

.0429 
•0343 

.0194 
•0155 

.0209 
.0167 

120  MACHINE    SHOP    DRAWINGS 

On  small  worm  wheels  the  teeth  will  be  undercut  as  in 
Fig.   78,  while  Fig.  79  shows  the  effect  produced  if  we 

/pitch  | 


FIG.  80.  —  Showing  Absence  of  Undercutting. 

turn  the  blank  small  (which  has  the  effect  of  moving  the 
pitch  line  out  nearer  the  ends  of  the  teeth)  the  undercut- 


THE    WORM    AND    WORM    WHEEL  121 

ting  being  increased  in  this  case.  This  gives  us  a  clue 
toward  avoiding  this  undercutting  by  turning  the  blank 
large  as  in  Fig.  80,  which  throws  the  pitch  line  nearer  the 
base  of  the  tooth.  This  wheel  was  sized  by  the  following 
rule,  which  is  used  by  the  Brown  &  Sharpe  Manufacturing 
Company  for  worm  gears  of  less  than  30  teeth: 

Multiply  the  pitch  diameter  by  .937  and  add  4  times  the 
addendum.  This  gives  the  throat  or  small  diameter  of 
the  blank.  The  large  diameter  must  be  laid  out  as  before. 
Figs.  8 1,  82  and  83  show  different  types  of  worm  wheels. 
One  hobbed,  one  cut  plain  with  skew  teeth,  and  the  other 
is  used  for  dividing  wheels  for  indexing. 

A  worm  can  be  run  in  any  spur  gear  by  setting  the  worm 
at  the  right  angle,  although  this  is  not  often  done. 

There  is  no  fixed  relation  between  the  diameter  of  the 
worm  and  the  speed  of  the  worm  wheel.  The  diameter 
of  the  worm  may  be  of  almost  any  size,  but  it  is  not  cus- 
tomary to  have  the  worm  less  than  4  times  the  pitch  or 
distance  between  threads,  but  it  can  be  as  much  larger 
as  necessity  of  design  demands. 

The  speed  ratio  between  the  worm  and  wheel  can  be 
varied  by  using  double,  triple,  quadruple  or  sextuple 
threads  as  is  sometimes  done.  This  means  that  the  wheel 
will  be  moved  2,  3,  4,  or  6  teeth  instead  of  one,  for  every 
turn  of  the  worm.  The  hob  must  be  of  the  same  pitch 
and  lead  as  the  worm  in  order  to  cut  the  worm  teeth  at 
the  right  angle. 

Small  worm  wheels  that  are  to  be  hobbed  should  be 
driven  by  positive  gearing  at  the  right  speed  and  not  be 
allowed  to  depend  on  the  hob  to  turn  them,  although  this 
can  be  safely  done  on  larger  wheels,  say  of  20  or  more  teeth. 


I22  MACHINE    SHOP    DRAWINGS 

Where  worm  wheels  are  not  hobbed  it  is  better  to  cut  the 
teeth  straight  across  except  for  the  angle  necessary  to 
match  the  thread.  In  fact  many  believe  they  are  just  as 
good  when  cut  in  this  way. 


FIG.  8 1  FIG.  82  FIG.  83 

Different  Types  of  Worm  Wheels. 

As  an  instance  of  this  we  are  all  familiar  with  the  Sellers 
method  of  driving  their  planers  and  know  that  the  screw 
working  into  a  plain  rack  has  given  excellent  service  and 
has  almost  never  given  trouble  from  excessive  wear. 


THE    WORM    AND    WORM    WHEEL  123 

For  dividing  or  index  wheels  on  all  kinds  of  machinery 
the  form  of  wheel  shown  in  Fig.  83  is  generally  preferred. 
It  is  a  neat  looking  wheel,  and  where  it  has  to  be  turned  by 
hand,  as  is  sometimes  the  case,  it  is  much  more  pleasant 
to  handle  than  either  of  the  other  forms. 

The  length  of  the  hob  for  any  wheel  is  not  a  fixed  quan- 
tity, but  it  should  be  at  least  one  thread  longer  than  the  worm 
which  is  to  be  run  on  the  wheel.  Worms  are  usually  made 
as  long  as  will  bear  on  any  of  the  teeth  of  the  wheel. 
This  means  a  worm  of  say  10  threads  for  a  5oo-tooth  wheel, 
which  should  be  longer  than  a  worm  of  perhaps  6  threads 
on  a  wheel  of  120  teeth  or  of  3  threads  on  a  3o-tooth 
wheel,  while  it  is  also  possible  to  use  a  short  worm  on  a 
large  wheel  it  is  necessary  in  each  case  to  have  the  hob  one 
thread  longer  than  the  worm  to  be  used. 


CHAPTER  VIII 

SKETCHES  —  ROUGH  AND  OTHERWISE 

THE  first  object  of  a  drawing  is  to  give  a  clear  idea  of 
the  shape  of  the  pieces  wanted  and  to  show  the  dimensions. 
While  a  finely  executed  drawing,  with  smooth  lines  and  nice 
shading,  makes  a  pleasing  picture,  it  may  not  be  nearly 
as  valuable  as  a  rough  sketch  that  has  every  dimension 
correct.  The  sketch  may  not  show  everything  in  its  true 
proportion,  but  if  the  figures  are  right  no  one  should  be 
misled  as  there  is  no  excuse  for  measuring  a  drawing  when 
all  the  dimensions  are  given.  One  of  the  best  things  to 
do  for  practice  is  to  sketch  any  tool  or  object  around  the 
shop,  such  as  the  anvil,  a  lathe  dog,  pair  of  calipers,  a  pulley 
or  a  hacksaw  frame,  so  as  to  be  able  to  make  a  new  one 
just  like  the  other.  This  teaches  us  to  be  careful  to  put 
down  all  the  changes  of  shape  and  all  the  dimensions  and 
to  be  careful  that  the  figures  are  right.  Suppose  a  back 
gear  on  the  lathe  breaks  and  we  want  a  new  one  made  that 
will  be  sure  to  fit.  Any  good,  bright  boy  can  make  a  sketch 
that  will  show  all  the  necessary  details,  can  measure  all  the 
dimensions,  count  the  teeth  and  have  a  drawing  from  which 
any  mechanic  can  make  a  new  gear.  It  does  not  matter 
so  much  how  it  looks  if  the  dimensions  are  right,  as  they 
tell  the  story.  If  no  draftsman  is  handy  the  gear  can  be 
made  from  the  sketch  itself. 

Take  a  plain  bolt  or  nut,  sketch  it  so  that  you  can  put 
124 


SKETCHES  —  ROUGH   AND    OTHERWISE          125 

the  dimensions  on  the  right  places  and  any  one  can  read 
them.  For  this  purpose  some  sort  of  a  perspective  is  best. 
This  cannot  be  done  with  complicated  pieces,  but  for 
simple  work  it  is  easy  to  make  something  that  is  often  more 
understandable  than  the  regular  drawing.  In  Fig.  84  no 
attention  is  paid  to  getting  circles  round  or  lines  straight, 
only  to  have  it  give  an  idea  of  the  general  shape  of  the 
piece  wanted.  Any  one  who  could  make  a  mistake  in 
making  bolts  from  such  a  sketch  has  no  place  in  a  machine 
shop.  This  shows  the  bolt  to  be  4  inches  long  under  the 
head  with  a  i3-pitch  United  States  standard  thread  cut 
i£  inches  on  the  end.  The  bolt  is  \  inch  rough,  hexagon 
head,  £  inch  thick  and  ij  inches  across  the  flats,  but  not 
finished.  Don't  be  afraid  to  put  any  information  necessary 
on  the  sketch  or  on  any  drawing.  It  is  better  than  leaving 
a  lot  to  the  imagination  as  some  draftsmen  seem  to  take 
pride  in  doing.  It 's  a  good  plan  not  to  put  the  same  dimen- 
sion on  twice  in  different  places  as  there  is  a  chance  of 
getting  one  of  them  wrong,  which  makes  confusion.  Have 
the  sketch  tell  all  it  can  either  by  figures  or  notes;  it  can't 
give  too  much  information. 

Fig.  85  is  a  steel  gage,  \  inch  thick  all  over,  2  inches  long 
in  the  main  part,  with  the  end  projection  \  inch  each  way, 
leaving  a  J-inch  corner  as  shown  and  the  round  corner  with  a 
f-inch  radius.  The  fillet  is  not  important  so  long  as  it 
is  rounded  out  enough  to  prevent  cracking  in  hardening. 

Fig.  86  shows  a  small  connecting  rod,  24  inches  center 
to  center,  which  is  the  important  dimension.  The  hole  at 
the  left  is  2  inches  in  diameter  and  at  the  right  it  is  3  X  4 
inches  for  an  adjustable  box.  This  opening  is  shown 
divided  each  side  of  the  center  so  that  the  total  length  of 


126 


MACHINE    SHOP    DRAWINGS 


A... 


Shop  Sketches. 


SKETCHES  —  ROUGH    AND    OTHERWISE         127 

the  rod  will  be  24  +  2\  +  3  =  29^  inches.  The  ends 
are  2  inches  thick  and  the  central  portion  is  round,  2  inches 
in  diameter. 

Making  sketches  is  also  splendid  training  in  another  way. 
It  teaches  us  to  be  observing  of  little  details.  Most  of  us 
look  at  a  thing  without  seeing  more  than  the  bare  outline. 
To  test  this,  lay  twenty  common  articles  on  a  table  or  bench, 
ask  a  man  to  look  at  them  for  a  full  minute  and  then  go 
away  and  make  a  list  of  them.  Seems  easy,  of  course,  but 
just  try  it  yourself  and  see  how  much  easier  it  is  to  forget 
from  quarter  to  one-half  of  them.  But  in  making  a  sketch 
we  have  to  note  the  details  and  we  remember  them. 

Let  me  again  impress  the  importance  of  not  forgetting 
any  necessary  dimension.  It  may  not  matter  much  if 
you  can  go  and  take  another  look  at  it,  but  it's  a  different 
proposition  when  you  are  sent  off  a  few  hundred  miles  to 
sketch  a  broken  piece  and  find  some  dimension  is  missing. 
You'll  feel  pretty  cheap  and  you  can  just  about  imagine 
the  complimentary  remarks  that  the  boss  is  making  to  him- 
self even  if  he  refrains  from  saying  them. 

It  is  not  the  object  of  this  book  to  make  draftsmen, 
but  to  show  a  boy  or  man  who  has  never  had  the  chance  to 
study  anything  about  drawings,  how  they  can  be  used  in 
every-day  work  and  how  to  read  them  so  that  there  will  be 
no  need  to  ask  the  boss  or  the  other  fellow  anything  about 
the  next  blue-print  that  comes  along. 

More  than  that,  it  is  handy  and  often  necessary  to  be  able 
to  put  your  ideas  of  a  new  tool  or  other  device  on  paper 
so  as  to  explain  it  to  some  one  else.  It  saves  lots  of  talking 
and  it  can  be  understood  much  more  quickly  if  you  can 
make  a  few  rough  sketches. 


128  MACHINE    SHOP    DRAWINGS 

The  sketches  shown  with  this  are  only  useful  with  pieces 
of  a  simple  nature.  When  it  comes  to  more  complicated 
work,  such  as  the  head  of  a  lathe  or  any  other  part  of 
machine,  it  is  necessary  to  read  the  regular  drawings  where 
only  one  view  of  a  piece  can  be  seen  at  once,  as  in  looking 
at  the  end  of  a  pipe  or  bar  of  steel,  or  the  side  of  a  machine 
which  may  have  much  of  its  mechansim  on  the  inside. 
But  that  has  already  been  learned  by  a  little  patience  and  you 
will  have  no  trouble  in  following  it  up  from  time  to  time 
with  practical  examples  along  that  line.  For  a  beginning 
let  me  suggest  that  you  make  sketches  of  various  objects 
in  any  kind  of  perspective  that  comes  easiest  to  you. 

Different  Kinds  of  Perspective 

It  is  a  great  gift  to  be  able  to  sketch  rapidly  and  correctly 
in  perspective,  as  you  can  convey  your  meaning  to  any 
one  without  much  chance  of  being  misunderstood.  But 
though  many  of  us  cannot  attain  to  this  we  can  cultivate  a 
little  skill  in  this  by  paying  a  little  attention  to  either  "iso- 
metric" or  "cavalier"  projection,  which  can  be  used  very 
readily.  In  the  isometric  projection  the  vertical  lines  re- 
main vertical,  but  the  horizontal  lines  take  on  an  angle  of 
30  degrees  from  the  horizontal  as  in  Fig.  87.  The  beauty 
of  this  kind  of  projection  is  that  you  can  draw  to  scale 
by  measuring  along  the  isometric  lines  and  lay  out  simple 
pieces  of  work  without  any  difficulty.  The  piece  shown 
in  Fig.  88  would  be  rather  difficult  to  sketch  so  that  a  black- 
smith would  understand  it,  certainly  not  without  two  or 
three  views  of  it,  but  the  sketch  given  leaves  no  doubt  in  the 
matter  at  all. 
Perhaps  a  still  better  example  is  the  steam-fitting  job 


SKETCHES  —  ROUGH    AND    OTHERWISE         129 


FIG.  87.  —  Isometric  Sketching. 


FIG.  88.  —  A  Sketch  that  a  Blacksmith  Can  Understand. 


I3o  MACHINE  SHOP  DRAWINGS 

shown  in  Fig.  89.  Try  to  show  this  in  the  regular  way  and 
see  how  many  steam  fitters  know  just  what  you  want  with- 
out a  lot  of  explanation.  But  the  youngest  boy  in  the  shop 
can  tell  what  the  sketch  means  without  a  chance  of  making 
a  mistake. 


FIG.  89.  —  A  Sketch  of  Piping  that  Shows  Just  What  You  Want 
to  Know. 

Another  kind  of  perspective  is  shown  in  Fig.  90  and  is 
known  as  the  "cavalier."  Here  the  base  line  remains  hori- 
zontal and  the  other  lines  go  up  at  an  angle  of  45  degrees. 
Some  modify  this  to  30  degrees  and  it  answers  the  purpose 
just  as  well,  the  idea  being  to  make  it  plain  and  not  to  have 
an  artistic  sketch. 


SKETCHES  —  ROUGH   AND    OTHERWISE         131 

Sketches  of  this  kind  are  being  used  in  many  shops, 
especially  to  show  the  toolmaker  just  how  new  jigs  and 


FIG.  90.  —  Two  Other  Kinds  of  Sketches. 

fixtures  are  to  be  made,  and  it  is  found  that  they  save  much 
more  time  in  the  tool  room  than  they  cost  to  make  in  the 
drawing  room. 


I32  MACHINE  SHOP  DRAWINGS 

Practise  a  little  with  either  kind,  laying  off  distances  by 
rule  if  necessary  and  getting  as  good  an  idea  as  you  can  of 
how  to  make  something  that  looks  like  the  piece  you  have 
in  mind.  You  can  buy  paper  all  ruled  for  the  isometric 
perspective  and  it  then  becomes  a  case  of  following  the 
lines,  using  a  little  judgment  as  to  curves  and  joints.  But 
it  is  difficult  to  make  a  sketch  that  will  not  be  more  clear 
to  the  average  mechanic  than  most  of  the  regulation  blue- 
prints, although  he  must  learn  to  read  anything  that  comes 
along,  and  can  do  so  after  the  many  examples  shown  in  this 
book. 

Handling  Drawing  Tools 

There  is  only  one  way  to  learn  to  handle  drawing  tools 
and  that  is  to  handle  them.  No  instructions  will  go  very 
far  in  teaching  you  much  about  them.  Use  ordinary  com- 
mon sense  and  do  not  forget  that  they  are  rather  delicate 
instruments  that  should  not  be  abused,  and  you  will  have 
no  trouble  whatever. 

It  isn't  necessary  to  get  an  expensive  set  of  tools  nor 
even  a  large  .set,  as  a  few  fairly  good  tools  are  better  than 
a  large  set  that  are  never  satisfactory.  For  about  five 
dollars  you  can  get  a  s<et  of  tools  that  will  answer  your  pur- 
pose nicely.  It  is  of  course  handier  to  have  the  dividers 
and  compasses  separate  as  it  saves  changing  them  from 
one  to  the  other,  but  you  can  get  along  very  nicely  with 
these  and  do  good  work  if  you  are  careful.  It  is  far  better 
to  get  a  small  set  and  have  them  good  than  a  large  set  of 
poor  instruments. 

Practise  making  circles  with  the  compasses,  both  large 
and  small  circles,  to  get  used  to  swinging  the  compasses 


SKETCHES  —  ROUGH   AND   OTHERWISE         133 


clear  round  the  circle,  and  spending  more  time  on  small 
circles  as  they  are  harder  to  draw.     Practise  placing  the 


.  Ordinary  Concrete  Coursed  Hubble 

FIG.  91.  —  Standard  Cross-Sections  used  by  the  General  Electric  Co. 

point  where  you  intend  to  instead  of  somewhere  near  it. 
You  will  find  this  specially  useful  in  drawing  in  fillets  and  in 
laying  out  work  to  see  where  you  have  sufficient  clearances. 


134 


MACHINE  SHOP  DRAWINGS 


Draw  curves  first  and  then  draw  the  straight  lines  to 
meet  them  and  you  will  find  it  much  easier  to  make  a  neat- 
looking  drawing. 

Draw  a  center  line  first  and  work  from  this  even  if  the 
piece  is  symmetrical  and  the  same  shape  and  size  all  around. 
The  center  line  is  a  necessity  when  the  piece  is  not  uniform 
and  should  always  be  used. 

Standard  Cross-Sections 

Although  it  is  customary  in  most  shops  to  put  the  names 
of  the  material  on  the  drawing,  some  use  a  standard  of 
cross-sectioning  or  cross-hatching  to  show  the  kind  of 
material.  The  one  shown  is  from  the  drawing  room  of 
the  General  Electric  Company  and  was  their  standard. 
They  generally  use  a  plain  cross-section,  however,  and 
•name  the  material  to  be  used  on  the  drawing.  There  are 
places,  however,  as  in  electrical  work,  where  it  makes  it 
much  clearer  to  use  a  different  style  of  cross-sectioning,  as 
then  we  can  easily  pick  out  the  insulating  material  from 
the  metal.  At  any  rate  it  is  well  to  know  what  the  different 
styles  mean  and  Fig.  91  shows  us  just  what  it  is. 


INDEX     . 

PAGE 

Addendum    85 

Angles,  something  about 59 

Angular  views  of  bars    58 

Assembly  drawings    17 

Back  rest  for  ratchet  drill 38 

Bench  lathe  head  25 

gears,  laying  out 107 

Boiler  setting  36 

Bolt  and  nut  13 

hole  table 77 

holes,  laying  out 75 

Broken  ball,  finding  size 82 

sections 16 

Card  drawing 20 

Cavalier  perspective 1 28 

Center  lines 5 

Chuck  screws 45 

Circular  pitch 9i~95 

Clearance 86 

Cross-sections,  standard 133 

Curved  surfaces 60 

Curves  cut  by  end  mill     '. 68 

Cutters  for  bevel  gears *. no 

for  spur  gears 105 

Cycloidal  curve 88 

Cylinder  drawing,  locomotive    40 

Dedendum 85 

Degrees,  table  for  rinding 72 

135 


136  INDEX 

PAGE 

Detail  drawings   17 

Diameters  of  pulley    77 

Diametral  pitch   9I-95 

Dividing  distances  equally 51 

Dotted  lines    5 

Drawing  tools,  handling 130 

Eccentric  and  eccentric  strap 43 

Elbow,  laying  out    64 

End  mill,  curves  cut  by   68 

Equal  spaces,  laying  out 78 

Examples  from  the  shop 1 1-25 

Finding  any  degree 70 

Five  sides,  or  pentagon    74 

Five  views,  where  needed 6 

Flange  drawing 47 

Flank  of  gear  tooth 86 

Four  sides  or  square 74 

French  drawing  of  a  worm    32 

or  metric  gears 98 

Funnel,  laying  out 62 

Gear  blanks,  size  of    92-96 

teeth,  generating 104 

laying  out    99 

shapes  of 87 

sizes  of    93 

tooth  cutters 105 

gage   104 

proportions   1 06 

wheels,  table  of  tooth  parts in 

Gearing,  rules  for 99 

Gears,  pitch  of 91 

Generating  gear  teeth 1 04 

Grinder  spindle  details 34 


INDEX 


137 


PAGE 

Handling  drawing  tools    130 

Helix,  drawing 66 

Heptagon s 74 

Hexagon 74 

Hints  on  laying  out 50 


Involute  curve    87 

Isometric  perspective 128 


Large  lathe  head 28 

Lathe  center •. 1 1 

head,  bench 25 

large 28 

Laying  out  angles 70 

out  bevel  gears 107 

bolt  holes 75 

elbow 64 

equal  spaces 78 

gear  teeth    99 

polygons 72 

sheet  metal   62 

spur  gears 84 

square  corners    53 

square,  hexagons,  etc 50 

work    50 

Locomotive  cylinder   40 

details 30 

eccentric  drawings 43 

Measuring  drawings   a 

Metric  or  French  gears :  98 

Monkey-wrench,  drawings  of 17 

Nut  and  bolt 13 


I38  INDEX 

PAGE 

Parts,  of  gear  teeth 86 

Pentagon 74 

Perspective    2,  18,  128 

Pieces  of  uniform  shape i 

Pitch  diameter   85 

of  gears   91 

Placing  views  in  a  drawing   '......  3 

Plan  view    6 

Points  to  remember 5 

Pressure  angles - 101 

Projection,  third  angle    y 

Pulley  diameters 77 

Ratchet  drill  back  rest   38 

Reading  drawings    '.  t 

Rules  for  gearing  . .                                99 

Screw  threads 80 

thread,  laying  out    66 

Seven  sides  or  heptagon 74 

Shade  lines   $ 

Shapes  of  gear  teeth   87 

Sheet  metal,  laying  out 62 

Side  outlet  for  pipe 66 

Six  sides  or  hexagon 74 

Size  of  gear  blanks   92-06 

Sketches,  rough  and  otherwise    1 24 

Solid  lines $ 

Speed  ratio   121 

Spur  gears,  laying  out 84 

Square 74 

corners,  laying  out 53 

Standard  cross-sections    133 

Stub  teeth    102 

Table  for  bolt  holes 77 

for  finding  degrees    72 


INDEX  139 

PAGE 

Tabulated  drawing   22 

Third-angle  projection   3 

Threads,  how  they  are  drawn 80 

Three  sides  or  triangle 72 

views,  when  needed    3 

Triangle 72 

Worm  and  worm  wheels 113 

threads    115 


MESA 
BRANCH 

DATE  HOUR 


TJ" 


NAME 





APR  22  £68 


0       I 


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